258 in a 61-63 american ?

Looks like GM bolt pattern from 4 cyl or V6. Put a five speed from an S10 behind it?

The firewall and trans tunnel need some work for a 258, but nothing terribly hard. You lose the factory heater though. ANY other motor will require some motor mount fabrication. WARBED here on the Forum put a 85 2.5L in a 59, which is the same as the 61-63 under the hood except for the firewall and heater design. The carbed 2.5L fits with no metal work. So will the TBI version. The  91-02 port injection intake won't fit without removing the left side hump, and might be tight then. The intake runners are much longer (to increase torque a bit at lower rpm) so the intake sticks out too far from the head. A carb or TBI intake could be modified to carry individual injectors by a machinist though, shouldn't be too hard or costly a job. Looks right at home in a little American!

Only the port injected AMC 2.5L is "too wide" -- due to the intake manifold. The las Ranger 2.3L and 2.5L fours are great choices. I don't know about the Toyota truck EFI fours -- they may have "wide" intakes like the AMC 2.5L. The carbed 22R will work, but the EFI 22R-E (82-95) might again be "too wide" due to the intake and throttle body assembly, this time on the right side. Might require removing the right side hump, but the intake and TB is kind of high on the head... might clear. There is a photo of a typical truck installation on Wikipedia.

lol, you're right! wrong section. i guess i slowly drifted OT...

and g-man's post... chop away! chopped out the entire firewall on my '61 and made it more or less flat. this pushed it back nearly 4 inches. and got all the fusty crap off the firewall.

i too have considered 232/258 in the american... but i'm no position to advise against foolish construction projects (they're often the best kind). an electric water pump *might* provide enough space to squeeze a radiator in front.  but it's tight even with the stock engine! i barely squeezed a thin SPAL in front of the radiator (absolutley not gonna go behind) and only after cutting sheet metal in the horizontal part behind the grille.