[Si Coe]

There were slippers before the Stealth box - but they tended to be slipper pinions (more like a nitro clutch bell) and therefore of limited use. Worked fine for protecting you from drivetrain shock but you couldn't really use them for traction control.
Stealth boxes didn't become available in the UK until the start of 1990 - I managed to blag one of the first customer ones into the UK off Ted Longshaw and got mine mid December 1989.
2.2in wheels worked much the same way - towards the start of 1990 Amark released pink 2.2in wheels for most brands. However except the very St Ive's specific Yokomo tyres everything was 2.0in so to use them we used to stretch out Schumacher 6x10 Cut Spikes over the carcass, which can't really have been better than a 2.0in rim.

I raced my standard gold tub RC10 with nothing except longer arms, one piece wheels and improved steering (RPM I think but don't remember) in the late 80's. Frequently my RC10 was alone in a field consisting entirely of Topcats, but it was totally competitive. That shouldn't be surprising as with those minor changes my car was essentially a Graphite but with the gold chassis.