The heads you have on there now are swirl type heads.... I have the same things and they aren't bad but then again not good like Vortec heads. I think they are 66cc... I cannot rememeber, I asked that question at www.chevytalk.com and they told me there. Go there to that site and ask Gchemist (sp) he knows. He posts in the section on like 70 something-87 trucks or so... I have a 85 Chevy truck so look in the catagory that fits 85 K10 trucks. He is in there and knows a ton about these trucks and subs like you got.