Ooooooooooohhhhhhhhhhh...
No yelling here, but a definite warning.
That frame is now a deathtrap. You removed a massive amount of support, THAN stuck a much more powerful engine in.
Its your bike, and your life... But please do some more research and have that frame properly braced. These 70s era bikes were flimsy and weak in the frame/suspension department to begin with and with the addition of a more modern engine, well I wouldnt want to ride it over 15 MPH.
Again, though, its your ass on the line. Just think about it before you go any further please. Dont want anyone getting hurt.