1972 Demon 340 engine mods

Well...

Motor swap is not easy as we are talking about a car that is in Europe, so access to everything is limited.
The idea was to use bolt ons, adding 100-150hp would be great.

I've seen some powerful low compression builds and was thinking that this might be the best option.
Looks are not the most important, there can be a compromise like new valve covers, intake, air filter, carb and stuff... Just non permanent mods.

I saw a set of ported, used iron heads with 270ish flows at .600 lift and was curios what cam/intake/carb could I use to make the most of it?

Rear end swap is also an option.