Block mods are simply shims fitted between the slots. There are now plenty of tuners on the block mod bandwagon just that JS tried to bleed as much money as they could from it.

ST tuning is plentiful and there is simply no need to go for any sort of custom mapping as there are packages catering for over 360bhp and more. Bluefin, Dreamscience, Collins Performance, Revo, JW Racing, Pumabuild, Pumaspeed all offer maps for STs and there are probably some more I've missed. Some maps allow you to run RS injectors too. Bluefin and Dreamscience do for sure. I don't know about the rest. You can expect 320bhp+ from bolt on mods and injectors before you start playing with the blower. IMO there ain't much need for well over 300bhp as it all becomes about how you put it down. Mine will easily spin all its power away if not careful enough and its under 300bhp. Get up to those power levels first before considering the RS Turbo route.