4 speed conversion

What blu said.
And if you machine out the bell opening, I can almost bet you will have trouble with centering the tranny to the crank. I highly recommend swapping the bell to fit the tranny, or swapping the tranny to fit your bell. And if you have a cam in the engine, I vote replace the OD tranny. And the reason is, that the OD tranny requires an engine with a wide torque-band, and the faster it spins with a tight LSA cam, the more this becomes apparent. They work great on a stock 318, not bad on a stock 360.
In any case you will need to align the tranny to the crank, so that they are on the same centerline.