About 5 years ago I rebuilt the engine on my YM1700. I had a blown head gasket but did realize and run it hot. Anyway I replaced petty much everything on the lower end except the crank and mains. I took the head to machine shop and they resurfaced the head and replaced the valves, steam seals, springs, etc. I replaced the cylinder liners, pistons, rods, and rings myself then put it all back together. It fired right up the very first time I tried it. I was probably lucky.
I will offer you some tips. This was the first engine that I ever rebuilt. If you don't have the shop manual get one. Study the manual carefully..several times. Take your time and triple check your work. It is easy to get confused. If you are not comfortable doing it yourself get some. You might try advertising for help on Craig's list too.]