300lb springs are on the heavier side of what most imp prod cars run, and will be a bit much for the street if it is a dual purpose car like you say.
what brand shock?
non wearing bearings?

that's quite a breakthrough!
how do they widen the caliper? I'd be a little wary of that - especially from a legal perspective. Check with an engineer before you hand over any money on those brakes. It might be fine (depending on exactly what he does), but I've never heard of anyone widening calipers before, and brakes are not something to take chances on.