I think you are best setting the duty first to reach the desired boost. Then up the gain to improve response so the turbo spools up nice and quick. Takes quite a long time and a long stretch of road in 3rd or 4th gear.
If you can't get use of a grinder, then a hack saw is your best option. If drilling out the spot welds, use a 10mm spot weld drill bit so you don't end up drilling holes in the cross member.
A friend of mine has an EP91 suffering from rust on the drivers side sill. He reckons the damage has gone beyond a repair patch so looking into outer sill replacement. Has anyone done this before and are there replacement sill panels available? Or do we have to find a donor?
I complained to J performance when this happened to me (was the pipe coming off the turbo in my case. They happily sent a replacement. Worth asking if the kit is supposed to be designed for the car, it should not foul anything. Worth a try...