OK - with 29" tires and a 3.25 (dang few of them as OEM's) will give you an effective ratio of about a 3.00 set of gears. A set of 3.00 gears with those 29" tires will give you about a 2.75 prairie (dog) ratio. I have 9''/3.25's in my roadster and hope to change back to the original 3.70's with my (also) 29" tires come spring as that 5.0L needs a little help. If it was me, probably not be in a hurry to swap out an 8" for that 9" - find a 250 cid Granada with 3.40s or 3.55s and you will be right in the right rpm range (also some Pinto wagons had an 8" diff with the same ratios). I never killed a decent ratio 8", tho I tried - often