I would think something will have to be done. 40 grams is a lot. (thinly disguised bump to the top)
Welcome to both of you to WG..
Martin in Australia is working on the 4V problem as we speak. Maybe he'll show up..
mine is 650, did not change balance, std pistons.rods crank
best ref here is MWren build of few years ago. think Mike /Todd ended up making new pistons or maybe shaving weight off 4v
But simple answer is yes balance crank
I found lots, most importantly, check everything, esp actual seat pressures, installed heights, coil bind etc, is not as simple as throwing valve springs in.
problems with mine far more from previous fixers than factory
interesting compression lario v targa, but do not know actual differences, parts book a good start.
but check clearances everwhere, assume nothing
Hope Mike chimes in, that bike might have miles on it by now
I have 600 on mine, all wot but not enough to make me the prover yet
check out my elephant walk thread for tricky adjusters, worth the dosh imho