That is the right serial for a shaved gear box from a 3.4 or 3.8Lwith O/D ---but to know what bell housing you have we will need to see pics. Before I went to all of that trouble and expense I would have a bit more than "a guy from a guy" as my safety. good luck.
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Psumably you could buy the flywheel and starter on approval? If the engine is out you could fit the box on ther back and check the starter and flywheel work with both bolted carefully in place using flat washers temporarily so as not to marke the parts.
I already said it in previous answers that it was a Moss box non-synchro first and will not fit your car without significant work. That work has nothing to do with the flywheel and starter and will still need doing regardless. Unless you are in a mad rush to get the car on the road I would be trying to get my money back and bale out of that box and buy the correct one.