To do a reverse jug you have to reshape the transfer port ramps in the case to match the transfer tunnels in the jug so the mix can flow from case to jug tunnels without hits a flat surface.
Its easy to see what has to be done by simply laying a base gasket on the case with gasket being turned backwards, this shows where and how much material needs to be removed.
Ive seen the totally open transfer mod and never like that idea, I match my transfers to a gasket that will not cover either opening case or jug, I usually always have to modify the gasket because my porting enlarges everything.
hands down so far the port work I have done to the 40mm steoke engine has got them to be much stronger and faster than any of the 38mm stroke engines I have running now, but I havent messed with the GT5 type much yet and the next one I build up will get some things done different than I have done so far and Ill see how that works out.