This means that you should change your oil more often to add life to your engine and avoid costly rebuilds. A few cans of oil and a pan gasket are whole lot cheaper than a bore job, new pistons and rings. Every 2,000 miles is a good average. After a while you will be able to tell, judging by how dirty the oil is, if you should do it more often or if you can go a few more miles between changes. There is a very valid reason for not venting your bike's rear end.
Pressure drives the gear oil into the pinion bearing.
If you vent the rear end your pinion bearings could burn up prematurely due to lack of lubrication. Drive shaft splines will also suffer from lack of lubrication. Yes, you should not have a problem. Through 1990 the valve settings are .006 intake and .008 exhaust. On all round head cylinders you will need to torque the heads first .