I wouldn't have thought they'd be that heavy in steering anyway being rear wheel drive an all? Is it worth the headache of fitting. My friend had a T18 and that was pretty light.. I suppose still an effort at parking lot speeds unless you're getting some rear wheel slip to help you round. Wider wheels/tyres won't help the cause. If the tyres are all old and crappy it will make the steering feel heaps heavier. On my old 929 i had crusty 195s and it was as heavy as. Got some mags with fresh 225s on it and it was tons lighter even though wider. Get wheel alignment also. Just thought i'd add 2c, you may want the psteer but consider what it will cost and effort.
All the best