5.7 0r 6.1 with msd hemi 6 and carb

I know XV sells kits for their conversion pieces that are "pre-tuned". I'm not sure how good that tuning might be, and I'm sure they wouldn't give you the exact numbers, but you might consider calling them to see if they can give you an idea about your timing issue. They may at least be willing to divulge some timing numbers to see if you're on the right track.