Wish I could help. I just went thru the same thing about a month ago when I installed my PTC convertor with a couple of friends of mine, and for the life of me I can't remember what size bolts I had to buy. I know they had a finer thread and slightly larger diameter than the bolts for the stock convertor. I didn't have a thread gauge so I actually hauled the convertor into the hardware store with me. I had some extra bolts left over (bought a couple of different lengths) and I just tried to check them with my tap and die set but none of my dies fit them. The one that came closest was a 7/16" 20 die but it was a loose fit. Thread pitch seemed just right but it was still loose. I'm not even 100% sure I was checking the right bolts but these were brand new bolts I had thrown in the box with my old convertor (same box the new one had come in). Best suggestion I have with the convertor & trans already installed is to find the tap that best fits the holes in the convertor (hope you have a better T&D set than I do), write down the numbers from it, and take that to the hardware store. Also, since everything's pretty much back together already you're not going to want to read this, but some flexplates will need to have their bolt holes enlarged slightly for the new bolts to fit through--I had to do this to one of the holes in my flexplate but it was out of the car since I was replacing it too. Good luck!
