I have a Dalton 300 ML, It was setup for a DA170, I would like to install a DA 200 what do I have to do to nose firewall. Can anybody tell me how cut off and do I need to change the thrust

I believe on mine I had to cut it back 2.5" perfectly all around then adjust the trust line after flying it.

A picture would help. A protractor is all you need to set thrust.

The DA200 is 54 mm longer. You must cut the motor box and get a new firewall. Some years ago I did it in my 37.5% Yak Carden.