It's an 8 3/4 rear with high quality parts. Mooser full spool and Mooser 35 spline axles. We tried a 4.30 gear but had the be the worst move we have ever made on the car. The car's combo is just a stock 340 with some w2 econo heads worked over alittle bit with some trw 13:1 slugs. It has steel rods and a very heavy 8 bolt crank. Just a mechanical flat tappet cam that I really know nothing about and ductile iron rockers. We are currently running 1 5/8 headers which we will be changing. It had a mechanical fan, water pump, fuel pump and alternator and a edelbrock 750 carburetor on it 2 years ago. Also a real messed up fuel system with 5.13 gears and ran a best of 7.56 with a 1.65 60 ft with alittle bit of traction issues. Over that winter I changed the following: Electric water pump, Electric Fan, Took off alternator, changed carburetor to a proform 750 street series it's black and silver and we did some work to it. Probaly only made it worse but we ran it anyway. Also added a intake spacer 2" aluminum open, Adjusted valves, and made some suspension tweaks and fixed the front end alignment and last but least we changed the rear end gear to a 4.30. We only got 1 pass which was bad so I have no real good data but the car went 8.00 at 87 was in 1/8 and 60 ft was 1.75 and 12.65 at 104 in 1/4. Car spun and we had the shifts messed up and a couple other small things but even if it didn't break the very next pass on the line like it did it would only run like maybe a 12.20 at best. Plain and simple it wasn't getting out of the 12's with that gear!!! I can't say it for a fact but I highly doubt that the 4.30 gear would work behind our combo. I hope this made everything alittle more clear?