The thing with the 066 and the 044 you would not need to modify them.
They are in a high state of tune to start with.

The 066 is 66cc's not a 100.

I don't know of anyone who makes a 100cc chainsaw.

At 17, I'd say make a working frame first, you may not need the engine.

You may be able to borrow one from a friend. At least for the testing.