What’s the best new high hp motor that will fit in a 72 Scamp?

Agree with Rusty on the LS
I just converted a motorhome from a 454 carb motor to a LS no comparison

hard to compete with 50 year old Iron
turbo or NA
There have to gen 3 installs, do a search
they are getting common at Junk yards

They are everywhere. And everything is available for them. Plus, they are a very stout design and can make a LOT of power without exotic things like stud girdles and the like. I'm still no fan, simply, because they are everywhere almost like a bad disease. But it is what it is. Their huge power for a little money cannot be denied.