what is the pumpkin (rear-end) size for rangers? 7.5 or 8.8? where can I get 4.11 posi-trac for one (I need to campare junkyard prices.

I'll answer the first one. 4.0s and Trailhead have the 8.8, evertyhing else has 7.5. Or so I have heard.

All Rangers are equiped with the Ford 7.5-inch rear axle with the exception of the 1990 & up 4.0-liter Rangers. These are equiped with the 8.8-inch rear axle. Both ranger rear axles come with 28-spline axles. Swapping a 7.5-inch axle for a 8.8-inch axle would provide a 35% increase in strength. The rear axles on all Ford Explorers are also 8.8's. These 8.8-inch assemblies use a 31-spline axleshaft. Increasing from a 28-spline to a 31-spline axle increases strength 34%. You can identify which axle you have by the tag attached to the inspection cover. If you use an Explorer 8.8, try to use a '95 or newer for the disks brakes.

Also unless you plan on using 35" tires and wheel HARD OR are planning on running a lot of horses you dont need to get the 8.8

If you want to get it anyway you need to relocate the spring perches which involves welding of course and having a shop mak your driveshaft fit onto the 8.8
Never heard of anyone having stock 4.11 gears in their rangers so that gear ratio will be more harder to find. look around for a 4.10 geared carrier and it would make your life that easier if you got whatever rear end you have now.

4.10 is what I meant and I guess what I am asking is do I have to replace the whole rearend or can I just go get the 4.10 and factory posi-loc unit?

So you wanna take the gears and traction lok out of the jnkyard pumpkin and then pay someone to put those in your pumpkin? WASTE OF TIME & $$$!!!!!!!
As long as you get the same rear end size that you got (7.5 or 8.8) then u just gotta take out the old and slip in the new.
Jack up the rear of truck, disconnect driveshaft, take u bolts off, drop the whole rear end, take out the axle shafts (2 of course) and slip those into the new rear end and then just put everything back together.