You may not need an adapter, just a stock bellhousing.
Not that familiar with T-10's, but they probably had the early bolt pattern on the case. The bottom holes in the trans should bolt up to the bell, the top holes are not as wide as the bell. You will have to drill and tap new holes in the bell housing if there is enough meat there (not sure about the aluminum bells).
If you can get a early 6 bolt bellhousing you may be lucky and find that all the bolt holes are the same (Not sure about this though).
There may be some issues with the input shaft length and the front bearing retainer which should not be a major problem.
This is based on my experience in adapting a top loader to a Y Block bellhousing which is some what different.