At only a -6 you may be asking for too much with e85. I only see Edelbrock making a -6 set.
https://www.edelbrock.com/fuel-rail-...nish-3634.html
I have -8 Wilson’s rails on mine fed by dual 450’s. My end goal is around 1200hp as well. I suppose it’s possible Wilson’s may already have the measurements for a Pontiac and will make you a set of -8 rails. You’d have to ask them. My conversion was done by my chassis guy using Wilson’s parts.
Wilson’s does the whole conversion with parts for around $950
https://www.wilsonmanifolds.com/page...on-conversions