My dowels were a straght 5/16. Once your gear lash is set you run your 5/16 reamer down through the hardened steel inserts in the milodon timing cover and ream the block to size. I got the info on setting gearlash on the milodon site. Cover fit very tight on the dowels when I was done but gearlash stays put. As far as TCI I am not sure, I did have to buy the longer hub for my ATI because the damper hit the cover.