Dwayne porter is the only guy I know you can trust for your porting. As far as your cam, I had a 340 with 12.5:1 pistons in it, I believe it was a true 12:1 motor, the cam I had in it was a Erson solid flat tappet 258/258-535/535-107. This was an awesome cam for that combo. I tried a couple other cams and was very disappointed. The Erson went back it. That cam pulled hard right to 7000rpm. I know your looking for roller, but just wanted to throw that out there if you decide on SFT. This combo used ported J heads at the time as well and was in front of a 4 speed. Hope this helps.