ACE,
Back to your SPF vs BDR - Specifically SBF vs BBF vs Coyote (that thread got shut down before I could play

).
Test driving each wont tell you everything with regard engine choice.
Just be mindful that something as subtle as tyres, or even the final gear ratio will make the "seat of the pants feel" very different, and incorrectly confirm a hypothesis or generalization.
Like I said earlier from what you have described, I get the impression that you aren't interested in ripping VC off, or tinkering with valves, or carbs or other, etc... So If I was in your position I would lean towards a BDR from Vintage with the COYOTE engine
As for your concern on how they sound... they all sound great
I dare say engine identification via sound, is a bit of a wank... 99.99% of the world's population wouldn't have a clue... and those that do, are most likely to be connoisseurs. They are likely to know your BDR aint a CSX3xxx, and are probably rev heads enough to be impressed you successfully fitted a new OEM motor in your new BDR.
Nothing against the SPF... but I see a BDR with a COYOTE in your future.
Again, this is just my take on you from your posts
Enjoy the hunt, its part of the fun.
PS: I wouldn't worry about the potential $$ lost either, the price rise will buffer that and the $10-$15k losses mentioned earlier on this thread are over many years. Just sayin'