I am very appreciative of all this help, I really am. I've never seen a babbitt bearing and was concerned when I ordered these parts off of eBay that I had just wasted yet another $40 on something that would sit on the shelf. But after reading your post (above) about the bearing shell, I ran back out to the shop. For ease of discussion, when I refer to the "old" cap, I am referring to the cracked one and when I refer to the "new" cap I am referring to the 70 year old part I acquired on eBay.
I took the new cap and installed the old bearing shell and bolted it to the block. Admittedly, I am not torquing down the bolts, just making them finger tight using a 3/4" socket by hand. With the old shell and the new block, the alignment was 99% perfect. The 1% is a a minuscule edge between the top of the block and the cap itself. The width of this edge can't be measured with any tool I have, but it is less than 1/32 of an inch for sure, probably less. I feel certain that between the paper gasket and some decent amount of gasket sealer that there would be no noticeable gap between this cap and the timing plate that bolts to the front of the block.
However, I am open to be proven wrong on fitment and/or the aftermath of passing along this new cap to my engine guy to have the whole thing fitted and line bored as necessary. I certainly would like this new cap to be the answer to my problem, but if it is going to cause some serious issue down the road, then I need to keep searching for a solution.
