BatmobileWS6

Im doing a heads and cam install (most likely G5X3 and ls6 ported heads) and with supporting mods hope to be around 420whp.
The previous owner tells me "hes pretty sure the gears are 373s"
How can I find out? Is there an easy way?
Thanks

2001NBMZ28

www.f-body.org/gears/

00BlueTA

iTrader: (8)

Pull the cover off the diff and count the teeth on the pinion gear(small one), then count the teeth on the ring gear(big one) and divide the two.

BatmobileWS6

ok Im beginning to think the car doesnt have 373s...I guess Im going to just get the heads and cam done...and if im not happy then change the gearing. Can I get the gearing changed at just a transmission shop or should I stick with a speed shop?
Is this something that should be re-dyno'd after installing when I would already have a custom tune?

Also, instead of starting a new thread maybe you could tell me noticable differences between 373's and 390's