Does anyone know if it's possible to powdercoat an r3 engine with all the innards still assembled (cases not split and disassembled). I'm told the engine would be at 450 degrees for about 30 minutes. It's very expensive to take the engine apart and gutted for coating. If the engine can't handle the heat being not running at that temp I'll go with having it painted, though not as durable.
Any help will be appreciated.

I would NOT suggest taking any aluminum block to 450 degrees. And I would not consider doing it to a fully assembled engine, the gaskets and seals will not handle the temps.

A good two-part epoxy paint is actually more durable than powdercoat, and will not oxidize as easily when exposed to UV and cleaning chemicals. Just make sure it will handle 250 degrees - many do.

Even if you pull the engine, any paint that is sprayed over fasteners and plugs will make these parts difficult to remove in the future without cracking the paint. Also, all nooks and crannies will need to be degreased if you want the paint to stick.

I hope this helps,
-WT