Id recommend you just work your 317's. Clean them up a bit and get a fulll radius valve job. Over 90% of the gains from a port job come from within 1 1/2 inch of the valves. A full radius cut on the seats, clean the bowl and valve boss, maybe backcut the valves, mill a little, and deshroud the valves. Should get a good gain. Go for it! Learning is great. I ported my own and am glad I did it.

 

I check CL like its my job lol, not much tho in the middle of Nebraska. I know i can find 317's so ill probably just go with that since there cheap and easy to find around here.