One of the issues here, is that when you do a swap, unless you are copying a swap that has already been done with full info from those previous swaps, you have to deal with various unknowns that could easily throw off any cost to benefit analysis that has been done to justify the swap. It's one thing if the swap is being done as a hobby project with virtually unlimited time, and no cost being assigned to the time spent. Its another if your time is worth something and the basis for the swap is a cost effective way to increase power.

You don't need to have one of our engines to get good power from a B20.
You do need an engine that's in good condition. You do need a modern cam design, designed specifically to enhance the characteristics desired, given the restrictions in the original engine design. You do need to cure some poor port flow issues. You should have a tight squish area ( piston to head distance ) to promote turbulence needed for good combustion and so you can increase or maintan a reasonably high compression ratio. You do need a better flowing exhaust system.You do need a distributor that's not worn out and that will allow you to have proper ignition timing.

Put some time and effort into these areas and you can easily have a 150 HP B20.

John
V-performance.com