So you want 2 go Big block...Read this first!

Phil,
With everything equal. Stock engines, no mods, just straight up swapping the engines, but both using headers.
I do think the BB would be slightly higher due to the price of the headers for the BB.
The trannies are identical except the cases, the rear would be the same, same for a radiator, conversion mounts should be very close in price, brake conversion the same, etc.
I looked the other day at the prices of the ProParts headers and they have gone up about $200 from 2 years ago. They are now over $600. I paid $450 for mine from the same vendor. Funny, but I paid $500 something back in the late 90's for the set I put in my Dart.