I had a 9.25 clutch in my original 67 Commando 273. It was weak and slipped a lot behind a 273. A larger clutch will NOT fit in that BH. Concentrate on finding 10.5 stuff and use that. There are plenty of factory iron and aluminum bells out there that will work.
My ‘66 273 came with a 9 1/2”, went with a 10” from Brewers after reading on Toolmanmike’s 273 build. I used the stock iron bellhousing, fit like a glove.
