I just started down the restoration adventure of my 1950 1/2-Ton 3100 and am considering an engine swap. It currently has a 235 and according to the previous owner it ran a couple of years ago. Originally I was just thinking I would replace it with a V8 but have since come to like the straight six. So my current debate is whether to proceed putting money into the 235 or bite the bullet and put it into something a little larger. Unfortunately there are no 261s to be found but I have come across a couple 292s for sale.
One of the 291s came out of a truck that the person bought to get the cab and other parts off of. The owner states there is a rebuilder tag and the head is off the engine and fresh bore new pistons can be seen. He did not however see the engine run . This person wants 800 for it. The engine casting number 93411147. I cant find much information on this number except the block does say "Hecho en Mexico".
The second 292 is believed to be from a 1981 and based on the casting number 93406004 is possible. According to the individual he bought it without seeing it run and was intending on using it but went a different direction. He wants 600.

Obviously there significant risk here but is there some checks I could perform to better ensure the engines were probably ok?

Thank you,

1950 Chevrolet 1/2-Ton 3100