Excellent advice , Patrick

Here is a slightly emended version of your list:

If you do find a 1955-2nd series or newer 235 or 261, be sure to consider/adapt-for:

1. With 55-2nd or later 235/261 block, use the 1955nd or earlier 216/235/261 short-shaft water pump (and Pre '68 Dave's water pump adapter plate that can be found on ebay)

2. Drill the front of the block for the front motor mount:
Tech Tip 1, and, Tech Tip 2

3. The 216 or pre-1955-2nd 235/261 bell/clutch housing may have to be used to match rear motor mounts (which changed in 1954 and changed later.

Also, the clutch-assembly must have matching/compatible parts:
- diameters of clutch plate and pressure plate
- pressure-plate attachment to flywheel bolt-holes line up
- release/throw-out bearing matched pressure plate

Tim
1954Advance-Design.com
1954 3106 Carryall Suburban
1954 3104 5-window pickup w/Hydra-Matic
The 216 and early 235 engines are not "splash oilers" -- this is a splash oiler.