A535/ NP2500 bellhousing

If it's marginal, you're on the right track.

As long as the aluminum is solid and not webbed or anything where the trans bolts will go, they drilled the same piece of aluminum for that trans, so there is no reason you couldn't set it up in a press or set a drill with a squaring jig from harbor freight or some place like that and do the same. Cut it with oil and use the right size bit for your tap, work the tap back and fourth every 1/4-1/2 turn and clean periodically with oil and you should be good. Aftermarket wheels have multiple bolt patterns these days and do fine under side and radial loads with the holes right next to each other.