If it's a UK 1.6, it's not a Torsen simple.
MX5- Drivers bucket seat. Welded diff. Whatever suspension. May as well chuck a set of hubs on it as they're only just over 100quid. Done. Don't touch the engine/exhaust/whatever as it's a waste of money.
Can happily do 3rd in the dry with the above, no need for more, just learn to drive it and you'll out-drift most 'better' drift cars as the owners suck ball.
Sold my MX5 fuckabout (the 5th one I've had) the other day to someone who's got a mental caged up FD RX7 and wanted a cheap beater drift car. I told him I find em more fun to drift than most other cars I've had even with 5 times the power, but he didn't expect it to be anything special, but soon changed his tune.
The car had what I always tend to do- Any old coilovers (cheapy ebay ones, shit but we're talking value for money here), welded diff, drivers bucket seat, and mintfab (£110 new) hubs. Nothing else, untouched engine.
The next morning he sent me this message...
"Fair play dude this mx5 is immense, so much more fun than my rx7. I was out in it till 12 last night, had too stop coz I was just going crazy haha. cheers man fair play"
Do the right mods, save your money by not doing anything else, and drive drive drive. More fun than pretty much anything.