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483 governs the imputed interest rule for your installment sale. 1274 would apply to a small partnership, similar in size to a 1244 (c)(3) size (equity of $1,000,000 or less). Or, a small partnership interest valued at $250,000 or less. 483 covers anything else.
http://www.irs.gov/publications/p537/ar02.html#en_US_2012_publink1000221706 is a link to the IRS interpretation of the rules.
From that publication: "Determining whether section 1274 or section 483 applies. For purposes of determining whether either section 1274 or section 483 applies to an installment sale contract, all sales or exchanges that are part of the same transaction (or related transactions) are treated as a single sale or exchange and all contracts arising from the same transaction (or a series of related transactions) are treated as a single contract. Also, the total consideration due under an installment sale contract is determined at the time of the sale or exchange. Any payment (other than a debt instrument) is taken into account at its FMV. Section 1274 Section 1274 applies to a debt instrument issued for the sale or exchange of property if any payment under the instrument is due more than 6 months after the date of the sale or exchange and the instrument does not provide for adequate stated interest. Section 1274, however, does not apply to an installment sale contract that is a cash method debt instrument (defined next) or that arises from the following transactions. A sale or exchange for which the total payments are $250,000 or less. The sale or exchange of an individual's main home. The sale or exchange of a farm for $1,000,000 or less by an individual, an estate, a testamentary trust, a small business corporation (defined in section 1244(c)(3)), or a domestic partnership that meets requirements similar to those of section 1244(c)(3). Certain land transfers between related persons (described later).Cash method debt instrument. This is any debt instrument given as payment for the sale or exchange of property (other than new section 38 property) with a stated principal of $3,813,800 or less if the following items apply. The lender (holder) does not use an accrual method of accounting and is not a dealer in the type of property sold or exchanged.Both the borrower (issuer) and the lender jointly elect to account for interest under the cash method of accounting.Section 1274 would apply except for the election in (2) above. Land transfers between related persons. The section 483 rules (discussed next) apply to debt instruments issued in a land sale between related persons to the extent the sum of the following amounts does not exceed $500,000. The stated principal of the debt instrument issued in the sale or exchange.The total stated principal of any other debt instruments for prior land sales between these individuals during the calendar year. The section 1274 rules, if otherwise applicable, apply to debt instruments issued in a sale of land to the extent the stated principal amount exceeds $500,000, or if any party to the sale is a nonresident alien. Related persons include an individual and the members of the individual's family and their spouses. Members of an individual's family include the individual's spouse, brothers and sisters (whole or half), ancestors, and lineal descendants. Membership in the individual's family can be the result of a legal adoption. Section 483 Section 483 generally applies to an installment sale contract that does not provide for adequate stated interest and is not covered by section 1274. Section 483, however, generally does not apply to an installment sale contract that arises from the following transactions. A sale or exchange for which no payments are due more than one year after the date of the sale or exchange. A sale or exchange for $3,000 or less. Exceptions to Sections 1274 and 483 Sections 1274 and 483 do not apply under the following circumstances. An assumption of a debt instrument in connection with a sale or exchange or the acquisition of property subject to a debt instrument, unless the terms or conditions of the debt instrument are modified in a manner that would constitute a deemed exchange under Regulations section 1.1001-3. A debt instrument issued in connection with a sale or exchange of property if either the debt instrument or the property is publicly traded. A sale or exchange of all substantial rights to a patent, or an undivided interest in property that includes part or all substantial rights to a patent, if any amount is contingent on the productivity, use, or disposition of the property transferred. See chapter 2 of Publication 544 for more information. An annuity contract issued in connection with a sale or exchange of property if the contract is described in section 1275(a)(1)(B) and Regulations section 1.1275-1(j). A transfer of property subject to section 1041 (relating to transfers of property between spouses or incident to divorce). A demand loan that is a below-market loan described in section 7872(c)(1) (for example, gift loans and corporation-shareholder loans). A below-market loan described in section 7872(c)(1) issued in connection with the sale or exchange of personal-use property. This rule applies only to the holder. More information. For information on figuring unstated interest and OID and other special rules, see sections 1274 and 483 and the related regulations. In the case of an installment sale contract that provides for contingent payments, see Regulations sections 1.1275-4(c) and 1.483-4."
483 is the applicable code section. Thanks for asking at Just Answer. I'm PDtax.