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Since Temco has been out of business for some time, it will prove difficult if not impossible to find the part by Temco part number.( PCOAO70H19)
However you should be able to go to an appliance parts store and explain that you are wanting to convert to LP and need a #55 orifice for the main burner.
Converting the valve on this one is pretty simple. Basically turning the fitting around on the valve.
See instructions on page 28 and 29 in manual at link below:
The unit has a #45 orifice in it for natural gas., That is .082 "
For LP you need a smaller orifice. The #55 is .052"
Threfore you want the#55 or .052"