I'm sure this info is on here but I'm too lazy to look it up. I'm removing the transfer case drop the p.o. put on cause to me if it's lifted a transfer case drop kinda defeats the purpose of a lift!! I'm just wondering about the right size bolts for the crossmember and the right size nuts for the transmission mount? I've got 5/16-18 flange nuts for the mount but they don't wanna go on easy and I don't wanna brake nothing!! Thx in advance.

 

Get yourself a Parts Catalog for your Jeep. It has diagrams
and the Mopar p/ns for about everything.Bolt and nut sizes
are usually given.
http://www.duriepuri.com/index.asp?id=187&idopen=187
You want the one for 97-99.

 

x2 on what Bob said.

Just to provide a bit of advice - be VERY careful removing the nuts from the studs - I ended up breaking both of mine off with what seemed like minimal force using a standard 1/2" ratchet. (Granted I think the P.O. waaaaaaay overtightened them.)

Were I to know what absolute hell that drilling out the studs and dropping bolts from above was going to be I would absolutely have put a lot of heat on the nuts before touching them with a wrench.
If you do end up breaking the studs, in hindsight I would definitely drill and tap instead of going in from above.

Those nuts are torqued to something like 150 INCH lbs IIRC upon reassembly.

EDIT - IIRC the tranny mount nuts are metric. Take the old nut to the hardware store and check the size properly - that's what I've always done.
EDIT2 - Try M8 x 1.25 for the tranny mount nuts - Parts catalog doesn't list the size, but this is what I found googling.
Try M10 x 1.5 for the crossmember bolts - same deal, no size in parts catalog.

 

Also the reason for the transfer case drop is to keep the drive-train in a functional alignment. So it's not so much a "defeating the purpose of a lift", but an unfortunate factor in lifting the vehicle over stock height.

People lift for various reasons, and increasing ground clearance may not be their primary goal. If it's not, the TC drop is an obvious solution since it can be done for less than $10 and a trip to the local hardware store.
Edit - Consider the fact that the TC, regardless of lift height is NOT the lowest component to clear obstacles - the axle housing is. It takes a tremendous amount of lifting before you get a substantial increase in this measurement.

The "proper" way to handle the drive-train angles (without lowering the transfer case) is to upgrade the driveshaft to compensate for the added height. (Which leads to the inevitable "I want a SYE to go with my double cardan rear driveshaft, etc, etc.") This greatly increases the cost however and may be why many folks prefer to do the lift and TC drop so they can get what they're really concerned about - bigger tires.