Didn't they have K10 Turbos in the UK??
I know what you're saying but I assume he just meant in regards to loosing traction with the increased torque. I only have 175s on mine atm coz my stuffed suspension was causing rubbing, but will put 185s back on once that's fixed. That's with just under 100bhp, hopefully be a little over once I get it back with the engine leak fixed and new exhaust.
There has been a fair few MA10ET original parts on Japanese auctions of late, might be worth investigating if you intend to go ahead with the conversion.
I'm only spouting theory here, but have you considered super charging? I assume you would only be wanting to run small amounts of boost so you could probably easily do say 9psi with a s/c and have no lag. From what I've heard its much easier to do a s/c conversion on a n/a car than it is to do a turbo conversion. Something to think about anyway... Good luck with it though, should be an interesting project.