Problem 1.
Driver's side window is broken. Cables are screwed. Does anyone know what type of cables can be substitutide for the stock ones without having to buy new regulator?
Problem 2.
Looking to do an engine swap away from the rotary to something better on gas, does anybody know if a 1990 model miata engine would work?

 

I don't know about the regulator off hand. They are quite a reliable part and don't often fail so there isn't much of a demand for them. Consequently, they are cheap on eBay and on this forum.

As for engine swaps, check out the "Other Engine Conversions" subforum. Obviously it would take a considerable amount of work and fabrication to make such a swap.

 

I had the same problem, i had to get a new requlator. the cable and mechanisim are rebuildable and i saw an ad for a place in NY that does it, but i found a new regulator and motor at my local parts store, from Worldpack, that was just a bit more, but was new in the box Mazda part.

 

I have heard of people using either motorcycle or bicycle cables. do a search, there are a few here that fixed their regulator.

I would rather put a V8 than a miata engine. so make sure you get a good engine capable of moving that heavy convertible.