the mounts for the H-9 planes work just fine you do not need to change the mount for your plane,both my H-9 warbirds have them and both run OS 91 surpass 4strokes drilling more holes in the firewall will weeken the plane more than the supplied mounts.
here's a suggestion thin some epoxy and brush some in the tank area especially at the firewall around the tri stock.
the only other gripe I had about the H-9's was some of the push rods were soft, I replaced mine with 256-rods for the elevator,and rudder.
the aileron rods were so short that it wasn't a problem.
other than that fly that bird.
more importantly when your getting ready to take off ease the throttle up slowly don't slam it these planes jump off the ground fast and fly really good.
my H-9's memorial day weekend flying solo at the field pretty quiet except for the hum of those 4strokes