In my opinion, it'd still be worth it. But I like old hemi's! :-D I also have a 291 Desoto. Get the ID number off of it, it should be located on the front of the block between the water pump and the valley cover.
Desoto's came in 5 variations- 276, 291, 330, and 341/345. The earlier 276/291 block is a "low deck", the 330/341/345 is a "high deck". Same block with different deck heights.
Parts are a little harder to come by, but they are true hemi's just like their Chrysler counterparts. The same sources will work for parts, and aftermarket intakes are now available for both low and high deck versions. Hot Heads has everything you need. On the plus side, either variation is smaller than a 331/354/392, even the tall decks, so they'd probably fit better. The 330/341's can easily make over 300 hp, some of the 4v versions did from the factory. Transmission pattern is the same as the Chrysler's. Engine mounts are the same as the 331/354/392, except over 1" narrower. I measured my 291 mounts just for fun, they measure 16 1/2" apart at the top holes. Same dimension I pulled off my '71 318, and the mounts appear the same. So, the mounts might even be easier on the Desoto. :-D Just for info, my 331 measured in at about 17 3/4". All those are just with a tape measure though, and the 291 still has a front cover so they may not be perfect.
You can find the specs on the Desoto's here
http://www.thehemi.com/engines.php
Casting numbers for the Desoto's look like this, the "S" number starts the ID, the first two digits tell you what it is.
DeSoto Hemi_________________________________________
S17 .......1952.......276.......Firedome....... 2-bbl
S16 .......1953.......276.......Firedome....... 2-bbl
S19....... 1954.......276 ......Firedome....... 2-bbl
S21....... 1955.......291.......Fireflite....... 4-bbl
S22....... 1955.......291.......Firedome....... 2-bbl
S23....... 1956.......330.......Firedome....... 2-bbl
S24....... 1956.......330.......Fireflite....... 4-bbl
S24A......1956.......341.......Adventurer....... dual 4-bbl
S25....... 1957.......341.......Firedome....... 2-bbl
S26....... 1957.......341.......Fireflite....... 4-bbl
S26A.......1957.......345......Adventurer....... dual 4-bbl
S27....... 1957....... 325......Dodge Engine....... 4-bbl
Heck, I have the engine out of my EL5 Dart, maybe I should pull the 291 off the stand and see if it'll bolt up, just for fun! :-D
