3RZFE into SW20

Why would you want to do that? It would not be worth the work for an extra 700cc, if you're unhappy with torque change your turbo. If you're still unhappy get a 2grfe

No matter how you look at it, if doing a v6 engine conversion, 2GR is the ultimate. 3RZ may be an ok engine, but for the work involved, 2GR is the logical choice. More torque & displacement from a 3.5L. In turbo guise, 2JZ 4-figure potential.

Engine conversions are good & all, but I'm a purist with the 3S/MR2.

A quick google search suggests that the 3rz is around 170kgs, and the 2grs are around 60 kgs less.

One thing to consider with putting a boosted V6 with more weight than the 3SGTE in NA form is weight transfer.
Its all great to stick a high revving 500hp engine in the back of the car but when you start adding some spirited driving to the package you will be in the 'danger zone' of loss of control far quicker than other options.
 
An example: After driving a 2GR-FE at Marulan driving centre on Monday, one of the biggest differences with the 3SGTE package is the weight transfer or lack of. This engine is at least 20kg lighter the mine and its very noticeable on the limit. It simply did not 'pitch' to the degree of my 3SGTE does. Far easier to tame so easier to control but I fear this could be a different scenario with an iron block in a MR2.
Lighter is better in these cars.
A boosted 1MZ or 2AR (Knightrous) or 2GRFE Supercharged would be a wiser option. BTW, the 2GR is capable of 500+hp at 6200rpm on low boost when prepared by the right people.
You will also need a E153 gearbox and decent axle cages.
Whatever way you go, we are all here to help.  

Thanks for all the input guys.
 
I just thought I would ask the question to get ideas so it is good that a few different ideas have been posted, thank you.
 
I have to admit when I bought my MR2 I purposely went looking for a 94 JDM because I wanted the gen3 turbo and all other updates that the 94's got, at that time I did not realize that the 3SGTE had the weakness in the block when pushed a bit harder which is disappointing. So that is why I started to wonder what options there might be out there because if I was to look at changing engines to gain a more reliable engine than why not look at options that will give you added gains at the same time and what got me curious about the 3RZ was the fact I had seen these push big numbers reliably and I also have a 3RZ bottom end sitting at my parents place.
But I do have to admit that I would prefer an alloy engine over a cast engine as it would be nice to loose some weight from the rear of the car and I would prefer to stick with a 4cyl over a 6cyl mainly just because I'm more of a 4cyl fan and love the idea of hypo 4cly's sticking it to their bigger engined cousins.
 
I do like the sound of the 2AR-FE that Knightrous suggested and I also like the idea of being able to run a EA60 6 speed with it! Out of curiosity which box would be stronger the EA60 or the 5 speed that is already behind my turbo?

While looking at alloy camry engines like the 2ar, you could also consider the 2azfe. Plenty common due to them being used in 2 series of camrys, as well as rav 4's, there are plenty of parts for them available, you can buy stroker kits, sleeves, even 1000hp crate bottom ends for them. Not as advanced as the 2ar, but a lot cheaper.

Yes my car is a genuine Gen3 hardtop turbo import and I did look for quite a while to find one that ticked all those boxes, preferably I would like to be able to just stick with the gen3 3S but I don't want to go building a strong engine and have the block fail once it is under a bit more stress.
 
To be honest I would love to eventually get the car somewhere around 300rwkw.