What Trans does my 72 Mach1 have?

Almost without exeption, the 351 2V had the FMX, and the 351 4V had the C6. The 302 2V had the C4.

After 40 years, though, there has been a lot of mix-and-match, all of these transmissions are physically interchangeable.

If it's got an iron main case and a removable bellhousing, it's an FMX. If it's got an aluminum case with a removeable bell, it's a C-4. If it's all aluminum with an integral bell, it's a C-6. Both the FMX and C-6 are tough as nails. The C-4's are the weak sister in stock form.

Hyjack

The FMX in my 73 351 2V leaks quite a bit.

I haven't done any diagnostic research, nor do I have any experience with transmissions (outside of swapping a C4 from an econoline van to my 72 coupe about 25 years ago).

Before I jack her up and crawl under there, what are the most likely problem areas and are the repairs manageable via a standard floor jack? I'm not likely to attempt any repair that involves removing the trans as I believe that's best left to a garage with a lift and a trans jack.

It's been a few years since this car's been on the road. Last I recall there was a vibration that may be attributable to an out-of-balance driveshaft.

I suspect the driveshaft as there are signs of some previous owner having a problem, specifically - there is a substantial gouge in the tunnel directly above the rear U-joint. I mention this as being possibly trans leak related.

All pointers and tips appreciated.

Also, repair/replace recommendations on the driveshaft appreciated. Assume normal street/highway use with maybe a trip to the track ... someday.

If it's coming from the front, it's the front seal. You'll have to pull the trans to change this (but it's easily accessed once the trans is out. Just pull the converter out and you'll see it. If coming from the rear, that can be changed simply by pulling the driveshaft out and changing the rear seal that the slip yoke slides thru. But if you also have a driveline vibe and a leak, the tailshaft housing bushing may need to be replaced, in which case you'll need to pull the driveshaft, then the tailshaft housing off, the bushing is a thin bi-metal sleeve pressed into the housing behind the rear seal. You'll need a new tailhousing gasket too, or you could just make one from gasket material and a small ballpeen hammer. Another leak source is the trans pan gasket, another simple thing to replace. Then lastly, there's the shifter shaft seal, which can be replaced by pulling the pan and unscrewing the shaft retainer nut inside the case, slide the shaft out and replace the O ring.