I have a good twin engine training plane for you until the the GWS-38 comes out. I took a GWS BN2 Islander & modified it to accept (2) Johnson 250 motors & MAN is this plane FAST!!
If & when the GWS38 comes out, I will be eyeballing the J250's for it if it is not too heavy.
P.S. - I am also flying a 21 OZ GWS A10 (Pusher) with (2) Johnson 250 motors with decent results.