Here's my very humble opinion. And I've said this before on this forum.
You would be settling with the 428. First, an aluminum FE can be made to look period correct. Just paint it, though I wouldn't. Also, the car will feel differently when driving (read BETTER) and faster with 100-125 lbs removed from the front end. The CSX and Pond aluminum blocks are beautiful pieces.
The Kirkham is one of the lightest Cobras on the market. It's aluminum and the engines should be too.
I can't remember if you mentioned this previously or not, but if you're opting to get the optional original-type suspension from Kirkham, then maybe the weight benefit of an aluminum FE would be a little less important.
People spend anywhere from $4,000-$10,000 on Webers to EFI, but for $5,000-$5,500, you can remove 100-125 lbs from your car and get a similar benefit.