Substituting Shelby block for Iron SO

[NSXDRIVER]

I'm the guy that just ordered the ERA. Been stewing for years over the whole SB/BB debate, and have elected to go BB. (Discussion of that point is NOT the intention of this post) I'm partial to the side oiler, but after pricing blocks and considering the inherent risks of paying that amount of money for a vintage part, I'm leaning hard toward the Shelby aluminum block. Here's my question: It seems that $10-12k is a good round number for a complete, authentic side oiler. If I am starting with an engine builder from scratch, and simply specify the Shelby block instead of the vintage part, will it have a dramatic impact on final price? Of a $12k side oiler, how much of that price is the builder going to tie up in the vintage block? I've noted that some builders have the aluminum block as an option, but at the $4000 mark, wouldn't this mean that the vintage part was only being given a $1000 offset against the $5000 Shelby option?