A535/ NP2500 bellhousing

Are you trying to use a slave cylinder?

It doesn't look like it obstructs the side cover access or linkage operation.

If that is all that is keeping you from using it, you could deal with the hole being off center from the raised mount area. If you used the transmission to guide a pilot hole, drill out the spot all the way through the other side and go with a bigger hole all the way through, then tap the bigger hole 3/4 through in the bell and install a threadded sleeve with loctite and JB weld the shallow side up a bit.

You could use the stock bolt size with a fix like that. JB makes an aluminum part repair epoxy that people use successfully with gasket areas on water jackets that is threadable, so it should work to fill that low portion in the trans to put a double threaded sleeve in place.