how to display 4:3 full screen game on widescreen monitor without stretching?
Right-click the port in your Porting Kit library, press "Wineskin Tools" -> "Launch Wineskin". In the window that opens, press "Screen Options".

Select "Override" instead of "Automatic" in the top, then select "Fullscreen" in the left and choose the "Resolution" that you want to use below.

Also, that port uses Mac Driver, which is incompatible with the configurations above, so uncheck the "Use Mac Driver instead of X11" box. Be warned: the game was tested with Mac Driver and not X11, so it may not work if you disable that box. If it stops working, you can repeat the process and check that box again.