My best pull was with the shops dyno headers, 2 1/4 primarys and if i recall a bit long. My 2 1/8 x 30 were down about 7 hp up top rpm. If I do ever get a set of 572/13 heads, my goal will be 1,000 to 1,025 hp. So I hope 2 1/8 to 2 1/4 step headers will be best, and what ever collecter is going to pull best in the mid range or overall. I am running a Torqueflite 2.45 low 1.45 second gears, 4.56 rear with 33 inch tall slicks. mph should be about 158, at 2900 lbs.Thanks for the input . A few calls are in order, along with taking stock of any more comments.