I did the same thing I had an old jetstream with a .10 in, swapped it out to a .28 direct drive. goes like stink. (well overpowered )

I just used some fibre glass resin from the auto parts store, mixed in with the glue I just added some chopped strand mat. clean the surface well, scratch it up a bit works fine.

for the engine mount I just screwed the engine staraight to a couple of blocks of wood and glassed them in also.