So the big thing about converting to a Tremec is fitting the Bellhousing. The Muncie or Super T10 or M22 Rock crusher were all loose transmissions. Right? I mean they had a loose ball bearing on the input shaft and it centered on the pilot bushing. The Tremec in stark contrast is made to precise tolerances and so it is extremely critical for the life of the transmission that it be centered with the crankshaft. Every second an engine is running the crankshaft is always trying to drive it's way to China and so when engine blocks get line bored in the rebuilding/remanufacturing process, the crankshaft always seems to mount a few thousandths lower. And if you have an engine block that has been rebuilt a few times you will likely observe that the offset dowels you will use you will clock downwards so that you can bring that pilot bearing into exact alignment with the input shaft on the Tremec. To achieve this you will use a dial indicator with a magnetic base stuck to the bare mounted flywheel with the bellhousing bolted to the engine. The dial indicator should be reading the inside diameter of the mounting hole where the transmission plugs into. And as you roll the engine you mark all around the bellhousing what the reading are. Then you can see which way is center and how much. And that is the point you will know what offset dowels you will need. This process is needed on ALL old school small/big blocks. LS engines were all designed in the days of the tremec and so they are all largely inside of spec without any special dowels needed.