Block should be ready later today. I've all but settled on a V4 to test.
Which makes sense. Test the unit with the fewest cylinders to keep work loads down and then IF it works as you like you can always build one with more cylinders when you have it as you like it.
How about a twin to begin?
I was originally thinking a twin, but after careful thought it struck me that the twin would have too many differences from the main design to be as good a test as the V4 would be. The bearings (which, incidentally, I am designing it to use the same bearings you'd find on the 426 Hemi, in order to add plenty of margin for strength) have to support two rod throws each, four pistons. A v-twin would only have two, which means you'd still not know if the crankshaft is strong enough because it would have half of the number of pistons per bearing. The dry sump oil pump is tied to the crankshaft as well, with the number of collectors being tied to the number of rod-throws. But with a v-twin, you'd have to design a different oil pump arrangement, not enough throws. With the V-twin and V4 you'd still need a balance shaft, so no advantage to the twin there. I just cannot find a real advantage to the twin beyond needing 35% less metal to make it.