if the oil pump had gone did you not notice a oil pressure warning light on the dash ? i've had two n/a and one turbo and the i think the 3sge / 3sgte engine are bullet proof as long as you look after them and dont rinse them from cold. the main problem i've had with all three of these cars is the clutch (general wear and tear due to miles on clock) distributors and alternators and i like to rev my cars up believe (no point having a sports car if you gonna granny it around right ?) have you been putting the correct oil in the car? have you added any dodgy additives ? and have you been keeping an eye on the oil level ?
The turbo engine is the ultimate in MR2's and you wont look back (especially if you put a few minor mods on like filter, exhaust, fuel cut deffender, manual boost controller and a proper boost guage!!!!) but you'll be looking to spend £800 - £1500 for engine, loom, gear box and all the other stuff you need and then you got to fit it or pay some one to fit (rogue systems are good, they do a fixed price install and also clean and paint engine and gearbox up like new) also take time to think about the install, i mean if the engine is out you may as well fiyt a new clutch kit, cam belt, fix the turbo hoses from hell and any thing else you can think of, least this way you get a top install with every thing working fine and peace of mind, working on these engines on that level is not so easy with engine in the car.
good luck and really do think about what i said, could you imagine how you would feel if you had the conversion and then found out the clutch started slipping 2k miles later, not good eh !!!!
Carl ........