Only if your a 6ft Blonde super modal.i will be delighted to give You a ride
Congratulations on the win, that's thanks enough for me.
Coolant leaking is probably a leaky hose somewhere. By all means do a compression and it will be interesting to see where it's at, but there would have to be something seriously wrong to be the block/head ie warped surface or blown gasket. So I doubt it's that as you have good power. I would start with the coolant hoses and make sure they are all secure. Don't forget the little ones from the thermostat housing as these are tricky and leaks often get missed there.
Great pics. 
(:-})
Without reading back through the thread, is it only the cylinder heads that have been rebuilt or have you had the engine cases apart. Did you check the pistons, rings and cylinder walls while the heads where off. Where both surfaces (block and heads) clean and flush before fitting new head gaskets. Any water in the oil? Just trying to figure out where it's at. Lets hope the garage can shed some light on it/understand what's wrong.
Oh and get some louder exhausts 
You should be getting loads more than that. I don't understand why the cyclone filter accept to help collect the dust particles. There's a lot of dust when your on track! Have you tried a standard filter box on the buggy and what sort of jetting are you running in the carbs with that cyclone filter. What size jets? These engines and carbs really don't like the filter being messed with and are very sensitive to changes. Talking about carbs are still using the standard CV carbs? I guess things are not going to work the same as if you had the engine in a motorcycle as it's designed for so it's going to be experimental and a lot of trial and error, but you should be able to get it running well eventually. Out of curiosity what weight is the buggy?