How to handle front Leaf Spring Nut?

Doing a lift on a 99 XJ. Started on the rear. Ran into and conquered the usual problems so far. Shock bolts broke, stiff leaf bolts, etc. I've Gotten the passengers side leaf out. Had a heck of a time getting the front leaf bolts out but between force, ignorance, and the helpful advice of the forums I got it. Went to Fastenal and ordered up 4 new bolts M14-2.0 x 120mm and a couple nuts, all 10.9 grade. Before I tried bolting up the leaf I checked the new bolt first. It threads in then gets really hard to turn.
What do we see as my best option. I was gonna get a tap and try and ream it out but of course I did some reading first.
My thought is that the nut is still attached to the frame. Either cross threaded or stripped. Judging by the bolt that came out that makes sense.
A) Tap the existing bolt
B) Cut the frame open and try to remove the bolt.
C) Drill straight through and put new nut on the other side of the frame rail.
???
Replies appreciated.

I'd try running a thread chaser (different from a tap) through it before anything else. A tap is a more aggressive tool than a thread chaser, meant to cut new threads instead of cleanup existing ones.
If that doesn't do it for you,
The weld-nut in the frame is on a sort of bulge coming off the main body rail. If you cut open the bottom side of that bulge and massage things, you can make a little window to stick a wrench up there. Hit that wrench hard enough or knock the old nut out with a punch, either way, get rid of it and you should be able to fish the new nut & bolt into place.
But seriously - try a thread chaser with plenty of grease / oil first. Failing that, maybe the tap. Cutting on the frame is always your last resort. Take it from a guy who's done plenty of rust-related hacks...

Can you put a mirror or camera up to it and see what it looks like? You might have some corrosion or rust at the end of the threads that could be cleaned out with a thread restorer, possibly a tap. I know taps get a bad rap here because they are more aggressive than thread restorers, but there are pros that clean threads with taps. You just have to be smart about it.

It'd be tough to get a mirror at it. It is the bolt that is welded to the inside of the frame. I'll try that when I get home from work.

Never heard of a thread chaser. I'll look into that. Thank you!

Worst case you can replace the existing mount with one of these. I've got an extra but unfortunately, it is for the passenger side (I broke the bolt). Installation isn't too bad but you will spend some time on your back. If you choose this route, I recommend a Sawzall. The good news is that you don't need to weld anything (but it is a nice piece of extra protection if you do).

Also note that those nuts are compression nuts and are supposed to be tight but not crazy tight.

http://www.polyperformance.com/shop/Synergy-Jeep-XJ-Rear-Spring-Hanger-Bracket-p-20685.html

Cut open the pocket and air chisel the existing nut off. Then when you are ready to install the leaf run the bolt in and thread a new nut on in the pocket. Make sure you make the hole big enough to get a wrench in there to hold the nut. I've had to do it quite a few times and it's worked great.

^this

Cut off wheel and chisel should work good for this?

If youre gonna use a regular chisel make sure u have a BFH to hit it with

Chisel should work fine. It's been my experience that those nuts are not very securely welded at all. A couple good whacks and I bet it pops off

Was a bit of work but I got it out. Angle grinder and a Harbor freight air chisel hooked up to my little 6 gallon compressor.
Now to try and put it back together...

The threads. No wonder it wasn't going through. Combination of dirty and corrosion was pretty bad.

The pic doesn't really show it but definate cross threading.