This is a copy from the Victory Library pages on deSoto engines:
"DeSoto Low Deck Strokers (276, 291)
There is no commercial crankshaft available for the low deck DeSoto motors, but it is possible to use the longer-stroke 1956-57 DeSoto factory raised deck 3.800” crankshaft by reducing the main journals to 2.375” to fit the smaller low deck main bearings, or line-boring the main saddles to accept the larger 330/345 main bearings. The counterweight OD may also have to be reduced to fit into the lower block - this will drastically change balancing, and may require either external balancing or use of Mallory metal.
The disadvantages of using the 3.80” crankshaft: reducing the main journal size reduces the journal overlap from .547” to .319”*; lower than any factory motor, but safe in my opinion. Boring the main saddles weakens the block, but saves money if you’'re installing a main girdle or new main caps. Which is best? I prefer to cut the crankshaft since it also cleans up any wear or damage, but follow your engine builder’s advice.
The 3.800” crankshaft’s larger rod journals must be reduced to 2.0625” if you wish to use the original 276/291 rods. There are other rod choices, but they will be limited by the narrow rod journal width (.931”) and short length required to fit in the low deck.
* Due to limited space inside the block, the full 3.80” stroke length may not allow the rods to clear the oil pan rails, outer walls and other obstructions. To get more clearance, reduce the rod journal size eccentrically inward to partially de-stroke the crankshaft down to 3.6125”. Going down to a 2.00” journal may allow 3.675” stroke in some cases. Heavier or longer rods will tend to reduce the clearance and require an even shorter stroke. "
There are lots of ways to skin this cat.
To me the easiest is to find a 3.8 crank and start measuring.
Connecting rods should be no problem at all. A 3.8 stroke in a street engine would like as little as a 5.7" rod, which coincidentally is the standard smallblock chevy length. The 2.0625" rod journal will cut down to 2.000, which is the early chevy smallblock size. Width should be easily handled by grinding the big end or by widening the journals when grinding the crank.
IF you didn't want to use the 3.8" stroke crank, the 291 crank could be stroked by offset grinding to a rod journal size of 1.850, which is widely used in the NASCAR world, sometimes called Mitsubishi size. That'd get you about 0.2" additional stroke, taking out to 3.6 or so.
Adney Brown of Performance Crankshaft in Michigan seems to have his name pop up when talking about custom crank work, including welded strokers.
Ohio Crank is also mentioned.
Paul in Devine, TX doesn't seem to be in the game any more. I heard a few years back that he was in poor health, he may be gone now.
If it was my $$$ I'd find a 330 crank and start from there, using a SBC 2.000" journal. You can get those rods weighing in the 550 gram range, which with a lightweight piston should make it easy to balance.
Also, a call to Hot Hemi Heads would help.
R.
