Twin 45's will only give you around 190hp flat out. You'll need 48's or 50's, or 48mm throttle bodies..
Consider that the 240RS, with 50mm mikuni's, 2340cc, 16 valves and the best parts money could buy only made 240hp back when...
Sure, they're getting 300hp out of a good FJ24 on the speedway these days, but who here has that kind of budget to throw around.
The L20b is a good engine, but it's always going to be a stump puller, and it's never going to be an FJ24....!
It's all about setting expectations!!