1) It technically bolts right on. All DSM TB bolt patterns are the same (I'm using a 1g NT for instance). The issue is that the hole in your 2g manifold is still 52mm, so the 60mm TB opening wont help you. Swapping to the 1g manifold requires a lot of porting to the head or thats completely ineffective (even detrimental), so you might as well then upgrade the head too. I Did all of them at once.
The best middle ground solution is to port the 2g manifold to 60mm. Its not hard at all, and if you like I can provide information on what carbide burs to use, where to get them, etc. But you need a die grinder, either electric (~80 bucks at sears, a pain in the ass), or pnuematic (~20 bucks at lowes/HD, badass, lots of control, but requires an aircompressor).
2) Not really. Its a straight froward swap. You will need to drain your coolant first though or you'll have a mess when you remove those lines.
3) The 2g stock elbow fits fine, most 1g guys upgrade that that one. Its not quite 60mm though, so it helps to enlarge that as well when you port the manifold.
4) You want a 91-94, since the vacuum line setup is very similar. The 90s are quite different, and the TPS is incompatible. You'll need to use the 2g Throttle Position Sensor since on a 2g it incorporates the throttle closed switch (hence the extra 4th wire) while the 1g uses an actual switch on the throttle arm (where the cable connects). Leave ths switch intact even though we dont use it, its also a throttle plate stop. It may stick shut occasionally if you remove that switch. Ask me how I know
I hope that helps!