I don't know how the Sideshow T-800 is assembled, but the T-700 has the jaw in a locked-in position, so it cannot ever move or be made to move. If the T-800 is the same and its jaw it angled to accommodate the long teeth, then a fix won't help make it look good as you would either have to have really large, long teeth in there, or leave a gap between the upper and lower teeth, making it look less menacing.
Yup. Plus, you will have to weather the heck out of the T-800 anyway, as the chrome job isn't accurate to the real props. Way too reflective. So either way, it's about what you think will be easier and look the best once finished. The T-700 has to be stripped, which is a PITA to do, the T-800 doesn't, but the teeth detracts a large enough amount for me to pick going through stripping the T-700 instead.
Plus... I got a damaged T-700, so I got it cheap. Bust sadly... they are listed on eBay at insane amounts right now. Definitely not worth that price. Anything beyond $350+shipping is way too much for this piece.
But everything has gotten really expensive on eBay these days. The old Tsukuda/Halcyon 1:9 scale kit that usually sold for $35 or less have skyrocketed to above $70 all the way up to way above $100. Insanity.
I know, I should have got a endoskull years ago. The SS clean version, with added rainbow effect is listed at £2000 on ebay these days!
Is there a technique for slightly scuffing the chrome finish, say on a cleaned up Combat version to make it less reflective, but without damaging it or exposing the resin beneath? I agree that a mirror like finish isn't the most authentic looking.
I would think that thin black or brown washes should bring the shine down if you do multiple passes and wiping it off each time. You can even hit it with a semi-gloss clear coat to get some of the mirror finish down - I think. I don't think you should start playing around with abrasive methods, such as sandpaper unless researching whether it will actually create the desired effect.