The upper ballhousing bolts take an E12 socket as I recall - replace the bolts with hex head 3/8"-16, with the same underhead length as the ones you're pulling out. (Amazing, isnt' it - how often those Torx sockets get used to remove soemthing, but not put it back in?)
I'd replace all the bellhousing hardware just to be thorough - I'm thinking the lower bolts are 7/16"-14, just for reference. Change the starter mounting bolts as well - one is 3/8"-16, the other is M10x1.5 (no, I don't know why, either.)
The clutch cover retaining bolts are 3/8"-16x5/8" (IIRC - just did this one a while ago,) and socket head capscrews work for this one just fine. You'll need a total of six, and they really should be change each time they're taken to bits. The U-joint straps are held on with 1/4"-28x3/4", use socket heads for those as well (since they offer a smaller head and internal wrenching, which eliminates interference with the straps. Socket Head capscrews are heat treated, as a matter of course, to SAE Grade 8 specs. And the smaller profile change at the head offers greater strength as well.) Use LocTite #222 or #242 on both the clutch cover bolts and the u-joint yoke bolts.
I'm not sure of the length of the flywheel bolts, but they're threaded 1/2"-20. If you get a length, please report back (the flexplate bolts are 1/2" long - the flywheel bolts should be a bit longer. Say, 5/8" or 3/4". I'm not sure if there is clearance to use socket heads there as well, but it's a common swap on other engines. The SHCS will replace all but the strongest "place" bolts out there - I'd not use them on a ring gear, but I'd use them everywhere else.)
I've not done the swap myself yet - but that's more due to a lack of an NV3550 donor box than anything else. I've taken down the BA-10/5 a number of times now...
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