Those 42-47 truck open rears will most likely be 3.78. All the ones I've had, been that ratio. Look on the center housing there will be two sets of numbers stamped on the ridge running parallel to the pinion, divide those and it will give you the ratio. Provided no one has changed the ring and pinion.
If you like, I can take a picture of where the numbers are. I have one mocked up in my roadster right now. It has 3.78 and a T5 behind a hot flathead. I have a Camaro T5 that I swapped the top plate and tailshaft housing of a S10 T5 on to it so I could have a 2.95 first gear ratio.
If you have a pic handy that will make it easier lol. Both of mine have some pretty thick paint. Haven't had a chance to get out and look yet. Brought the T5 home. Not sure how many actual miles are on it, there are signs that someone has opened it up before so it may have been gone through at one time. Had a brand new clutch and pressure plate which of course I won't use. Anyway it feels nice and tight. I'll pop the top cover off at some point and see what it looks like inside.
The Jalopy Journal
