I've drifted my MR2 in the clubman competition 3 times this year, well twice as it broke down 15mins before the final round. I've come 4th and 2nd, so it is deffinately achieveable.
Mine is a pretty standard uk spec car (yeap only 165ish bhp and a :dermal: open diff), running induction kit and custom exhaust. And it sounds as though I have the same suspension as you have
Get yourself some strut braces to stiffen it all up as best as possible.
You do need to be quick in the MR2, and it is very unforgiving. Do slightly too much to get it sideways, or force it to transition to quickly, and it will spin. However, I feel that learning to drift my MR2 has taught me so much about weight transfer.
Alot of the turbo's came with an LSD as standard, although it doesn't provide much lock it has to be better than my :dermal: open diff. Check yours by jacking up the rear of the car and spinning 1 of the wheels, if the other goes in the same direction you have a diff. If it goes the other way than you have a open diff. It is possible to drift on an open diff, but its behavior is a little unpredictable. If you have the money than get hold of a TRD diff
All this said there are some simple facts that you must take into account.
1. You WILL NOT be able to hold as big a 'drift-angle' as you would in a front engined rear wheel drive car. The weight behind you means that holding a large angle is all but impossible, once it goes beyond a certain degree, you pretty much going to spin.
2. You CANNOT transfer/transition between drifts as quickly/aggresively. Again the weight behind you means that the rear of the car will have a lot more momentum than a front engined car. Throwing it in a transition is easy enough, but catching it can be a problem. If you are too aggresive than it will pretty much spin.
Once you understand these points, and practice lots and lots, you will learn to 'feel' just how hard you can push it.
Look through the media section of this forum, download and watch Clubman round 3 and 4, as well as some of the conedodgers days at Andover. There is some footage of me in the MR2 in those vids.