DD
Sounds like you have a lot of good suggestions and options. Complete tear down & rebuild, new motor build, or keep the bottom end pretty much intact and swap out the cam, heads & intake / carb. What you ultimately wind up doing, will likely be dictated by the budget.
One common theme is pull the motor. More work up front but easier in the long run. Want some help ??? ... would be glad to lend a hand
tkb