Unless you have a compelling reason not to - Stock Eliminator, Mopar street car, purist, budget - 9" is always the right answer for a race car.

Gear selection, all steel housing, easier to work on, aftermarket support, lightweight parts, stronger when properly done, pinion lower in the carrier, etc.

On the street though, Mopar guys see that diff cover from the rear and they know you aint playing around. On a race car it sounds like the 9" may be the way to go.

I will need a 4.56-4.88 gear. What’s the difference in weight? So many answers on google and they all are different. Is the 9” 100 lbs lighter?

When the 9 inch is made as strong as the D60 the weight is the same or so close it doesn’t matter. The D60 at the gear ratios you want to run takes less power to drive.

Unless you need to swap gears all the time the Dana is the way to go.

Call Cass. When he broke it down for me, the choice was easy. He sells both and will be happy to build whatever you want. Also, he knows all the mopar pinon offsets and stuff that you may not get if dealing with other dealers. I purchased mine complete with his brakes. Has been trouble free for 11+ years under a 10 second B-body street car. Will likely go 9's this year.

https://www.doctordiff.com/

That ratio is available for the Dana. If you are going to be changing gears very often then you should buy a Strange S60 since they are much easier to work on. The cheapest option is to find a used Dana 60 in a wrecking yard and have a local shop cut it down and put gears and a spool in it. If it was me I'd put the Ford Torino ends on it with the Set 20 bearings so you can get rid of the Mopar adjuster. The Torino ends will give you a ton of brake options. Since it is a ladder bar car you don't need the pinion snubber mount so no need to pay extra for that. If you don't have a local truck shop or chassis builder who you trust then you might need to order it from someone.

i will call Cass next week and see what he recommends. i have bought stuff from him before and is a super nice guy to deal with.

i won't be changing gears from weekend to weekend. good chance i'll end up with a 4.56 ratio.

i was looking at the S60.

You might be able to find a used one for sale. I sold the S60 from my Duster for $1900 last month. It had 4.10 gears, Detroit Locker, 1350 forged yoke as well as Ford Explorer disc brakes. I also had a spare set of 4.56 gears and a bearing kit for sale. Complete package deal was $2100. I didn't get too much interest on it but finally sold it to a guy who was building a S10 pickup.