Hi Rita,
How've ya been?
To be honest, I'd be wary of a used overdrive transmission unless it came with a guarantee. Even if it does you can't expect your mechanic to remove and reinstall one for free should it prove bad. If an overdrive gearbox is what you really want, I would look for the whole package as a rebuilt unit with all the goodies to adapt it. Will this be pricey? Yup.
Of course, you could accomplish the same thing with a five speed kit. There are two of which I know. First, there is the one sold by our host and others which uses the Ford Sierra gearbox. Then, there is the unit which uses the Nissan 280Z gearbox. This kit is sold without the transmission by Rivergate Restorations. You must supply the trans yourself, and they are getting a little hard to find, though there are still some out there. Both are good, well engineered kits with nice strong gearboxes.
Whichever way you decide to go, if at all, it'll make a real improvement in the car. We've done all three, and folks genuinely like the results, in spite of the price. If I can be of further help, let me know. Feel free to email me if need be.
Also, what's ever happened to your search for an MGA?
Glad to hear from you,
Bill
Motorbill
From Lola to Land Rover, If it's British and has wheels, it's likely I've bloodied me knuckles thereupon