I've doing the same kind of thing. In imperial, my front track is about 41" I think. I've gone for rack and pinion but only because I found a small rack on eBay for not much money. If you're used to driving a car with several turns lock to lock, you might want to make your micro similar. A steering box may be easier for you to fabricate but I'd look to see what parts are easily available first. Remember you may want spares in the future too.