I thought about leaving the barrels in place and just hoping that the old gasket will hold. Dealer’s mechanic suggested that’s not the best choice. I guess he’s right, especially when these jobs are done first time by an amateur.
Finding best practices about rebuilding engines with removable cylinders blocks wasn’t easy. Below few links showing rebuilts by fitting cylinders from the bottom of the barrels
Hayabusa cylinder block install
Suzuki GSX 1100
Honda CB750Honda CB750 barrels uneven low
Yamaha XJR1300
One note about rods side loading: best practice seems to be to level pistons first, lower barrels slowly then engage dowels. Now thinking if I need three sleeves. Or maybe side loading is more theoretical and one sleeve would do.