What kind of engine mods were needed to make the 40-45 hp? And are the other pipes you mentioned hard to find?  And how much would one expect to pay for each of those pipes?  What are each of those pipes best suited for?

I would have to look for the blueprints if I can find them.  I have not tried to build any of those engines in probably 25 years or more.  There was not any black magic in those engines or any of my engines.  The trick is to get everything working together.  ALL OF THE COMPONENTS, ports, pipe, head, carb and ignition have to work in concert with each other.  There is NOT ANY ONE COMPONENT that is responsible for making the majority of the power gains.

It is not uncommon  to spend over 200 hours in developing an engine to perform at that level.