The car is a stock '75 Cutlass with a 350. I thought it had a TH350 tranny [with a leaking speedometer cable] so I ordered one of these:



Then I get under the car and look, and it appears to have one of these:




After some googling it appears the same as what's in TH400's and 700R4's. Maybe somebody put a different tranny in it at one point? Are all those housings that look like the second one the same? I don't want to order ANOTHER part that doesn't fit

 

Same housing for TH350 and TH400. Not sure what the one you got is for.
Also the numbers on the housing correspond to the number of teeth on the driven gear that work with that housing. There are two different housings for use with different diameter driven gears.

 

After a little googling, it looks like the speedo housing "bullet" I got was for a Cheby TH350 and the BOP TH350's use the other larger kind. Okay, so it seems like the larger kind only comes in 2 varieties depending on speedo gearing across BOP TH350's, TH400's, and 700R4's then? I just crawled under and looked at it and it's got 38 and 39 stamped on it, so I guess that's the kind I need. Guess this is what I need then?

http://www.ebay.com/itm/PLASTIC-SPEE...-/310372614159

 

That one should work. I've never seen that first type before, but then again I've always owned Oldsmobiles.
Personally I'd rather have an aluminum one.

http://www.summitracing.com/parts/tci-880022/overview/