Send it to a builder. A site sponsor.....
if you insist on building it yourself, talk to a builder, send them you jugs for over bore/port work, buy a cool head (whatever you want to call it) and the 4mm crank. get domes cut by said builder to match pistons/stroke. Follow builder recommendations on carbs/jetting/exhaust...... assemble it, break it in and ride the wheels off of it.