Bob...here are my answers:
1. I'm pretty sure the TNT MKV bearing well is the standard
1" diameter. The TNT MKIV bearing well is 1 1/4"
and the hole needs to be enlarged, but really isn't that
hard to do unless you have the MKIII stainless steel plinth.
It can be done, (I've do it several times), but requires a
lot of patience and a pretty sharp enlarging bit and a
variable speed drill. You need to go slow when drilling
stainless steel. I burned up 3 drills the first time I
tried this before I figured it out.
2. It will be a MAJOR upgrade.
3. Same belt
4. Most tonearms require the "Super Armboard",
but the SME IV already is a pretty tall arm and should have
plenty of travel up and down. The regular armboard is
1/2" thick the Super Armboard is 1" thick.
5. You will probably need to change out the springs to
compensate for the extra weight of the platter. If you
could find the SIMS, that would take care of that.
Hopefully VPI still has the needed springs?
The difference between the TNT MKIV and MKV platters is the
MKIV is 1/3 delrin and 2/3 stainless steel. The MKV is half
and half. I have both and think the MKIV to be better
sounding, but the MKV is very good and will be a great
upgrade to your MKII platter.