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Hi Bonnie, The only one that will work for the '78 is the TH350 due to length issues. Preferably you want one out of a vehicle that was 4wd so you do not have to change the output shaft to run the transfer case adapter. The company I recommend for al the supplies is Novak conversions. They can assemble an entire package for you to perform the change easily. I'll post a link to the products you'll need below.
I suggest calling their pre purchase line first to get all the info ***-***-**** they can then transfer you to sales.
I've been using their products for quite some time and find they are superior to other companys in the adapter market.