Yes, I have to agree - Mazda a much better engine and the gearbox is particularly good - far better than the Type 9 or MT75 that Ford's use.
However, it's always going to be tricky on a tight budget and, personally, I would hate to have to start with someone else's half-finished project. I guess suggesting you buy a 2nd hand chassis (often come up on eBay etc) and start from scratch is a non-starter? You could re-use anything decent on the S7 (suspension, brakes etc?) but then you get a modern chassis and you can re-do everything the way you want it?