I have to go with the others on this as well.
My M-body was well known to have vapor lock issues and the lines really couldn't be moved.
The factory-recall answer was a small electric pusher fuel pump just after the tank. It worked.

I installed a full-blown electric fuel system on my M and have had no issues.

But- You will never get your tuning sorted out until you solve the vapor issue.

Good Luck,
CC