The YJ runs Dana axles. Theres a tag between two of the cover bolts that gives you the axle ratio.

Yes, it's the math all driveline shops use.
rpm=(mph x axle ratio x 336) / tire dia.

The above is for a normal 1:1 ratio high gear trans. If you're using an OD trans and want hwy RPM's you'll first need to multiply the axle ratio buy the OD gears ratio(usually around 0.70-0.75)
Also the "336" constant used above is for manual transmissions. I don't remember what the constant is for AT's but a shop like Randy's Ring and Pinion can tell you.
Also keep in mind stated tire size is larger than actual when you get into large tires. 33's are really closer to 32's.

My original idea was to just get a Mb motor and then mate it to my jeep tranny and then have diesel don and a friend of his make the plates to mate the motor and trans. i have recently been looking at other engines because a diesel this size just doesn't have that much power.

i really wanted the fuelmileage also don said he would help me for free swaying my opinion.

recently i was looking in to putting in a 460 and if it is possible. i really wanted the dana 60 because it is just wider. i didn't want it for its strength.

For your question on the whole mating tranny and motor or t-case make friends with the nearest tool and die shop. or if you know anyone that has autocad to make whatever partyou need. tool and die shops make alot of parts for truck companies they are very reliable.

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Kaleb, 17 years old. I own a 1988 jeep wrangler. it has a carburated 4.2 liter. it also has an automatic. I bought it all stock from a man that had it for a couple of years and had bought it from the original owner. when the guy dropped it off it was driving some what good but not the way i test drove it. i put alot of new things in it, the list is:Radiator, water pump,fuel lines, fuel filter, plugs and wires, egr valve, pcv valve, jet and seat. i think thats it.

You're working at opposite ends here...one sentence 'fuel mileage' and then 'not enough HP' but the dsl only has 8? HP less than the 258. Then you mention a 460 as in Ford 460? which blows the entire "fuel mileage" thing out the door. If you plan a 460 you'll not only need the D60 rear but a D60 front axle swap also. There isn't one piece of running gear (front/rear axle, trans, tcase) in that 88 YJ that will hold up to a 460 with any amount of offroad, hot rod use. Yeah you can build/scab some redneck buggy thing together and shortly after wards destroy it and it's then a redneck lawn ornament. If you do a 460/YJ swap so it'll actually work and be somewhat reliable you better have a lot of skills, suspension knowledge and a pretty decent job for a 17 year old.
I think you need to sit down and think which direction you want to go. You really can't go in the "want fuel mileage" and "mega HP" directions at the same time. Then get out some paper and a 'sharp' pencil and figure out the costs of the direction you've chosen.
Keep in mind the old hot rodders truism. "Speed costs money...how fast you wanna go?"

the cj frame is pretty light.

a 460 will twist that little pup like a pretzel.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.