First off, not all the info is correct in this thread.
Unless you have crank end play. Don't worry about swapping.
I've owned multiple 7bolt cars that have made deep into the 450whp range.
If you do decide to go 6 bolt, for say the sake of making big power. I'd suggest buying a block thats totally stock, seeing as you never know what kind of corners a person may cut on doing assembly to say its built and it turn out to have stock components instead.
I'm on my...9th DSM currently and I can answer any question you have on them.
Good luck with your GSX, get you a 14B, or 16G, a 190LPH fuel pump a set of Evo8 Injectors and a intake and downpipe and you'll be impressed with how the car will act.
Tune it on DSMlink for maximization of the mods