Very interesting points here, much to learn yet. The photo posted above by "vintageford" is especially intriguing.
I recall an article from several years back (90s maybe?) in that other big model car magazine that compared 3 or 4 readily availble kit engines, and I believe the consensus was the Johan had the best proportions and captured the look best, but wasn't without fault, and that the best solution was what you are attempting here; mixing many parts from different sources. For me, it all boils down to the topside and front proportions, as most of the block will typically be hidden.
Very good work you're doing here, and plus one for resin copies! (Would prefer it sans intake, to keep options open)