You don't need a boost controller or a thicker spring, just put a needle valve in-line with it so you can crank down and limit the amount of boost your WG sees, it's a poor man's boost controller, and there's almost no limit to how much boost you can make. A close friend of mine is a Saab fanatic and he's currently running a primer-blue 1986 Saab 900 chassis with a boosted 2.3L engine to 47PSI of boost this way. He had to lower the compression ratio so low first to take all that boost.