Any GM dealership. I bought mine from www.crateenginedepot.com along with 6 longer bolts. Scoggin Dickey at SDParts.com: Performance Parts, Racing Engines, Racing Engine Parts, Race Engines, Race Engine Parts - SDPC will have them also. Another place is 700R4, 700 Raptor Transmission from PATC, 700R4 4L60E 48RE 4L80E . I think Hughes sells a slip on extension that goes on the old 60e converter pilot and slips into the 6L crank.