Retro! When I got back into TC racing around 2010 I bought a job-lot of BDs for not very much cash. Kept me and the girlfriend going for a few years.
New spares will be impossible to find now. Keep an eye out on ebay for a second car or job lots of used spares.
In general it's fairly strong. The worst bit are the inner hingepins. They're only 2.5mm which is too thin and they bend easily. I replaced them with 2.5mm drill blanks instead which are much stronger.
Wouldn't have a clue about gear ratio. Start with a random pinion. If it's too slow, fit a bigger one. If the motor melts, fit a smaller one
