I believe it's a super t-10 tranny and yes they did come in cast iron. Never heard the lack of aluminum being the reason. I'm getting one tomorrow that is cast with a one inch cross shaft(same as M-22) . M-21 and M-20's came with a smaller 7/8th's cross shaft. That might be called counter shaft, the one below the main shaft. Doesn't a t-10 come with a bigger output shaft like an automatic tranny? That would be bigger than the 20 and 21. Anyhow, it's a strong tranny that I have dragged with in the past(450HP) and never had a problem with. Easy to rebuild too.