i would buy some .600 lift springs if it was my engine since the x cam is a .542 lift and with 1.7 roller rocks it would be more then a .550 lift so it would put .550 springs in a bind so i would buy .600 lift springs
Contact Thumper460. He sells double valve springs for stock heads that are good for .590" lift. That is what I am getting for my heads as well. I think he said something like $130 shipped. Don't quote me on that though.