Very good points if the gearbox on the 600cc is weaker then
even at 500kg it will be a problem. The only way to secure
a cheaper big motor would be to go get it from America as
the local 1300/1400 motors are very pricey. Problem is the
duty and the rest unless it can be brought in with other
stuff by container like Caseys Dad or some other mobs do.

Any opinions on a modern V-twin Suzuki 1783cc twin cam
multi valved with a shaft drive therefore big capacity
with less hp then boosted.
The Suzuki Boulevard is 360kg dry so two riders, packed
and fueled can reach 200 extra average so 560kg.