I am not familiar with Megatech so I cant help in regards to the engine. But if you were able to start it before you moved the LSN, you should be able to start it again.

First, get hold of the manual and find the way to reset the LSN to factory setting.
Second, remove the glow plug and eject the excess fuel that you flooded the cylinder in trying to start it. That is what is causing the tightness at the TDC. This is best done with an electric started, watch out for the spray of fuel.
Thirdly, change the glow plug. If you havent used it for some time, the plug is likely no longer useful. I am not sure whether you can use a #8 or F-Type OS plug in that, check.
Fourthly, check your fuel. I have noticed that the idle becomes more reliable with some nitro in the fuel. I suggest 5-10% and used synthetic lubricant if you can, engine will become cleaner running
Dont try to handstart the engine the next time, use an electric starter. I have found that even reliable OS engines will not start the first time with handstart and we only get more frustrated in the process and give up earlier
If nothing helped, ask a club expert to help you.

If all else fails, only then buy a new engine. The exercise you did will not be in vain, it will help you on the OS and it will help you become more comfortable with engines

Hope I helped and best of luck

Ameyam