I did the Surge tank and two pumps tucked under the rear end. It works fine but was a pain in the arse to fit.
Modify the stock tank if you can as FKN16V says. Or to get started you could just run a high pressure pump straight out of the tank. It is a bit dodgy, esp. when the tank is getting empty, but I know a couple of guys who run it like that and their cars still work.