For what it's worth...
I had a GSXR1100 air cooled motor in an off-road minibuggy several years ago.. As you would imagine, it had ALL of the power you could want, and in my case, I never had issues with it overheating (which was an initial concern).. Having said that, the engine was not stuffed under a hood with poor airflow- it was well ducted
and hung out in the open, and it also had an oversized oil cooler (which worked well)..
So if you can get good airflow over the motor, I think I'd default to the air cooled lump as you said weight is a concern (and assuming you don't plan to run it in the desert for hours on end
)
Worst case, if it does give you issues, you can always swap the water cooled unit in..
Good luck, and post pics of what you do
--ccrunner
_________________
Dean
1972 Honda N600 Restomod "ccrunner's N600 VFR800 repower"
1963 Volvo P1800 Restomod
http://locostusa.com/forums/viewtopic.php?f=36&t=163091959 Berkeley SE492 Restomod...
viewtopic.php?f=36&t=19397"ccrunner's 1960 MGA coupe Restomod" found on MGExp.com