[big gear head]

The hole in the bell housing is what lines up the transmission with the crankshaft. If the hole is too large then the transmission will not line up correctly and it can damage the input shaft, gear, bearing and pilot bushing. It could also damage the pilot area on the main shaft and cause the gears to break if it's off a lot. There is about .440" difference in the hole size between the car and truck bell housing, so there is a lot of room for the transmission to be out of alignment, depending on how much clearance there is in the bolt holes. Maximum recommended out of center for the transmission is about .005".