Andrew first make sure that you get plenty of heat in to the engine, and if you can keep the heat gun on it while you try to start it that will help. Also its importnant to note that you have to give it time for the heat from the heat gun to work its way into the crankcase not just the head.
Also this is very important, Get a large regular screw driver, so when the engine does stick, you can stick that thru the flywheel hole and pry the engine unstuck. That way you won't have to remove the engine from the car. Remove the glow plug completely and pour a lot of after run oil into the engine, then heat it up and bump it a couple of times. Pour in some more after run oil put the plug back in it and don't tighten it all the way.
About the fins breaking off, The Go engines have the best stock cooling head on the market, its has a large diameter, lots of fins, and still very light. You will notice when your Go engine shuts off that the head will drop almost 100 degrees in a very very short time. This is one reason its very important to place the piston at BDC immediately after the engine shuts off because the temps will drop very fast.
This type of performance comes at a cost and while I have not personally seen the fins break or bend any easier then any other engine mfgr. I can understand how you could be upset if 8 people at your track had the problem. But in reality if that many people bent or broke cooling heads at your tack than there is something in the track causing it.