[Lynn Eades]

Radek, It doesn't really matter what engine you use, but a later one with 3 3/16" bore (239cu in) will pull better. Better again is the same block with a Merc crank which has a 4.0" throw (255 cu in) In this guise your carrier will pull away at lower revs, and be more "tractable"
What you want is the bigger cubes so that you have more low down torque.
Your photos hide the details.
There is another hole in the back of the block, up hill from the ones in the cast lug, that the oil cooler connects to. This is hidden by the inlet manifold which is a post war?, or if not, then a late war one. (oil filler in the side near the front)
You need to go to "Vanpelts" flathead V8 website. It will give you heaps of info.
The three holes in the center of each head face can be used to identify the year of manufacture.
The crankshaft has only one oil delivery hole in each big end journal, which means you have to use the expensive , full floating bearings. Depending on the year there are two sizes here (also two types of con rod)
If you find a crank with two oil holes, it will have the large journals, and can take the lock in bearings.
The above refers to a 90 or 100 h.p. engine.

The 85 h.p. engine is 3 1/16" bore, floating big ends, has the core plugs in the sump face of the block. It probably has a raised (actually cut away around) inlet manifold mounting face. It could be, but may not be a relieved block (it has a low bit going into the bore around the valves)
If your engine block takes the small journal crank, it won't take the big one (it is an 85 h.p mtr)
The oil is filled from under the breather at the rear of the inlet manifold.
The inlet manifold was probably a cast iron one.
The sump will not have a removable part for fitting the big clutch, and it won't fit in a carrier with the sump that has the removable plate on the bottom.
Your block appears to have no core (welch, frost, or expansion plugs) in the sump face. I think that stopped in 1942, so your block could be correct.

Please back up what I have said with your own research.
I hope this helps.