Pickup replacement shouldn't be complicated, however when I was modding my old 7321 I realized that base plate of my new pick up is slightly different and screws weren't aligning with old holes, so I had to fill old holes with epoxy and drill new ones
Also I replaced the nut with graphtech nut (I believe on their website it was described as Carvin 7 nut)- it was wider than the original so I had to sand it down a bit. Also string spacign is slightly different from the original, but not significantly. And obviously you will have to do some action adjustments on the nut.
With lockign tuners there might be only one problem - you won't be able to fit heavy strings in some of the locking tuners. I had to drill a larger hole to fit 0.68, but again that was nothing major or complicated.
Stripping the finish will be the most complicated part - time consuming and somewhat painful (but that depends on your tools and aproach)
If i had a beat up 7321 right now, I'd do the same mods