Everything I have looked at points to red top beams at the moment.
As long as the engine isn't 'too' dishonest it won't matter because it will be copping an entire rebuild.
It seems like a good starting point, and fully building it will still cost less than a supercharger. :P

I haven't started my Beams swap yet, its sitting in the shed waiting for me to have time lol, so i can't really offer any advice yet. I bought a MR2 half cut with a redtop Beams. It cost me heaps to buy and get into the country though. I think i might have been better off buying a motor, engine loom and ECU from an Aussie supplier in hindsight. You should read Mandalays build on this forum. He's gone to the extreme with his car...he's supercharged his Beams, and his attention to detail is unparalleled.

The same gearbox will be fine. If you get the engine loom with the original ecu, you should only need to do a bit of repinning of some plugs. It should be a bolt in changeover otherwise.

Tacho modification shouldn't be too hard. I have a friend who has done lots of it. The trouble now is saving for one, then finding one :P 

Well the power increase in just the redtop is pretty decent. I'm actually not sure what to do with the suspension a whole lot. Wheels are perfect, but are brake and suspension upgrades a 100% neccesity? I've given the car a pretty good run on a couple of roads and the suspension set up in my opinion is pretty tops.

It may be best to buy one already converted. If not, there is no easy way out of spending a fair amount of cash.
There is a conversion kit available for about 2k landed. It has everything you need for the conversion bar the balance of the exhaust. 
Highlander has the contact details of a guy in Qld who will make the system for you at a fair price.  
Best to use a E153 gearbox from a MR2/Celica/Rav4. One of the guys makes conversion kits for the front wheel drive gearboxes.
MR2 Turbo axles/hubs/brakes are also required.
If you have a turbo car, you are on the right path. If not, you may need to buy a wreck and strip it for parts.
You can buy an engine with a loom from as little as $1000 but it will need to be refreshed. There is also a risk of the rear bearing letting go which means a crank regrind. At this stage, you would strip it down, chemical clean it, some new rings and bearings which will be a big plus for you. while its apart, you may as well strip the head, clean it, reface the deck and head to avoid a head gasket issue. Then spend some time with the sander to maximise the flow of the exhaust ports, port match the intake plenum to the head and a general clean up. So with some elbow grease and another $2500 you can give the engine a mild refresh, get the comp back to factory levels and add some more ponies with the porting or you can buy a low km engine for $3400-$4400. I would go for the refresh option.
Make sure you buy an engine with loom/ECU and immobiliser .
You can then wire this into the MR2 loom.
You will need to add a electrical component to sort out the tacho.
There is little more to it, but it will be a weapon on the street. I have driven a track SW20 with the 2GR and it was a dream to drive. It has under 200rwkw but it had plenty of grunt. Better balance than the 3SGTE, excellent power delivery, start it and go for it then turn it off and forget about it. Really great value.
Also drove the beams 2.0ltr. Another great engine package for less money but it does not have the poke of the V6 and it something you have to experience to understand. When you come over to MTC 2015, hopefully we can organise some passenger runs so you can do your own comparisons.