4.30 or 3.90 gears for a 8 3/4 rear

I have a low milage set of 391's from a Duster approximately 30k. I had the motor at carlisle on a run stand. The motor sold.

I am using the housing to rebrace another rear for a Race car build. I am Keeping the 4 spd set up. The carrier is still in the housing. It is a 391 suregrip. 489 carrier. I drove the car once a year since 1979 then into the shop to strip it last year . The rear is sitting in one of the race trailers complete drum to drum.

I will sell the carrier complete for a reasonable offer. I live in Pa. They ship in a double bucket truck freight. pretty cheap. I have several out but I know this rear is a bolt in ready to go small joint . I only recently decided to use the housing for the Demon due to a new style bracing we are using. I am selling the braced housing that was from my other Duster that we have in the Demon now for set up. I have other 391's. but do not know there history. I also have ratios