Standard form 130 about the same as a Sprint.
Probably gain a couple from running the engine without a cat, but it'll be pretty close. They go well enough to be fun - mine certainly does. It also leaves a fairly large area on the exhaust manifold side that looks like it needs a turbo in.. Hard to tell from the pic but the rear axle still looks 1500, which could be cutting it a bit fine strength-wise. MX-5 engines are pretty bullet proof - short of the hydraulic lifters getting a bit rattly sometimes they don't tend to break. Parts are cheap and available
A good project if someone doesn't mind a bit of structural welding (re-enforcer between the front seats has been cut out). Worth a go if anyone is bored!