A 292 will require modification to fit in a Thriftmaster truck, since that engine is from the 1960s-1970s trucks. The experts will be able to give you the details.
The 261 is nearly a bolt-in fit. You might need to use your bellhousing from your 216 or 235. Also use the 216 water pump and adaptor plate from "Pre-68 Dave" on ebay. PM me if you want to see pictures of what mine looks like.
