GM 8.5 8.6 3.73 10-Bolt Ring & Pinion Factory........Will these work with my 91 350 9ci rear end?

Im trying to make a street machine out of my stock 91 350 any suggestions?

If your '91 has the 8½" 10-bolt, they should work. Be aware that you may need to order a "thick" ring gear if you have a 2-Series carrier. I know the later 9C1s and Impalas have the 8½" Saginaw axle, but I'm not sure about the '91s. If you haven't opened it up for an oil change lately, this might be a good time to do so.

Thanx for the info....but what exactly do you mean by "thicker"? How do i know if thats what ill be ordering?

Any suggestions?

what is the current gear ratio? I would suspect2.93 or numerically higher, heck a 9C1 might even be 3.42 already.
The comment blue made would not apply then, it is an issue with 2.56 and maybe 2.73.

A 9C1 will already have the 8.5" axle but some civilain cars got 7.5" axles.

He already has GU6 which is 3.42 (std with the LO5 in a 91 9C1). I already suggested keeping the 3.42 and spending the money on something useful (exhaust).

I had 3.42s in my car and for daily use actually prefered them to the 3.73s and this is on a WELL modded LT1 that likes to rev.
With the TBI and that fact you already have 3.42s I have to agree stay with them.