Sorry to hear of your 2smoker woes! I really like my 4 stroke, though my 2 stroke is a little more powerful. I there existed quality pistons, rings and wrist pin bearings for the 2smokers they would be alot more reliable. If I had the $$ I would like to develop a "longevity" kit for them consisting of the aforementioned parts (and a few more).
Also, a little insight that I have learned here from the pains and troubles of other members... That inner tube sandwiched between the front motor mount and frame tube is not a good idea. It will lead to broken engine mount studs and may even cause the frame tube to crack over time.
Good luck with your 4 stroke build! I am betting that you will like it alot.