i would like to know what is the best engin for it

Search in WARBIRDS FORUM, much has been said about this plane. I summarize by saying a G-38 or other comparable 40 cc engine will be most excellent in it. You'd be shooting yourself in the foot to put an OS 1.60 in it. Any warbird this size deserves a good gasser.

Zen G-38 and this bird make a GREAT combo and no holes need to be cut in the cowl except for the down-pipes of the muffler. My friend has smoke in his as well.

This was my WM 80" Zero. Flew great, used a G-38 and Century Jet retracts. 18 pounds.

A 1.60 will pull it around in a very scale like manner but I suggest a healthy Moki, BGX or the Gasser.