The 250 mounts like a modern small block, from the sides and the tail shaft of the transmission. Nothing from the 235 will work with the 250. You are going to have to fabricate mounts or adapt V8 mounts to the 250. I am not sure how the '59 transmission mounts, but I would be willing to bet you have to make a crossmmber to hold the 700R4 tailshaft. The driveshaft will be wrong to, its unlikely the length and yoke will be right for the new combination.
