I run a set on my 750. They are a pain but do work. The female threads near the push rod tunnel are not up to the task and must be replaced with inserts not (recoils). The oil return hole needed rework on mine it caused a leak letting oil find it way under the spigoit lip and than to the large conter bores for the socket head cap scews. To this day if I hammer on the bike while the oils cold I get some leaks.
On the plus side you can run .0015 total clearance on your pistons. And you do save a lot of wt. They also use the thru bolt design of the 850 even in the 750 size much stronger. Mine ran 500.00 US funds . Be sure and check the total hieght of the jugs mine were -.040 from stock bumping the comp. a bit. Everyone who sees mine running who has owned a set themselves askes how I keep mine from pouring oil out. You have to hone these to fit the pistons while fully tourqued with plates or they will not work and this drives many away from there use. If the honing is done without plates assembely of the motor will distort the bores at the top. norbsa
Another problem with Al barrels is the sleeve is an interference fit. I personally know two guys who have had the sleeve slip in use. Not good! These were from different suppliers...one from Left Coast Racing and the other from Norvil. I wish they had a better reputation, for the benefits norbsa mentioned above. 5 Franklins is a lot of $ for a product that could potentially wreck the motor. I'm not racing so I'll stick with cast iron.
The sleeves slip when they install them by using nitrogen chill and not heat. The trick with sleeves is to press them in hot and keep them under the press till they cool all the way. Most slipping is downward and only blows a head gasket. I have never heard of this blowing a motor only time and doe. norbsa