[Yukon Jack]

Here are two links for the article on using the later crossmember.

link 1

link 2

Burt4x4 used this type crossmember when he put in his 454 and had to do very minor firewall mods. He does have a 3" body lift I believe.

I stock with the stock crossmember on my 69 K20 and had to make major mods. You can see info on my swap on my website listed in my sig.