Laysons is the only source I could find that had the old pinions remanufactured (probable not any longer). I have never seen a 20 tooth pinion available anywhere but a 21 tooth was used for 3.23 manual shift cars. I have salvaged many 18 tooth and one 19 tooth but I was never able to find a replacement for my 21 tooth pinion. I have salvaged them in A and B body cars, trucks and vans built until 1965. Brewers sells used 16, 17, 18, & 19 tooth pinions but said 21 is very rare.