Try to be careful with language, some of the things you say aren't very clear, but I understand if you are new to this the language is new also.
You say the rockers have back and forth motion? I think you mean vertical because they are not tight enough between the blocks? You are going to need a torque wrench set for 25 foot/pounds. When you have both rockers loose and one side is ready for adjusting the valve lash you can loosen the two nuts holding the intake or the exhaust rocker and squeeze the blocks together. Hand pressure should work on a /6 but some find the need a little more pressure from a set up of sockets (to clear the rocker shaft) squeezed by a large C-clamp or large pair of pliers. Do one at a time either intake r exhaust then do the other. This way you will not have to tighten the nuts down in a stepped pattern like was done when the gasket was new because you have only two nuts loose at a time.
There are a couple of ways to determine which side is ready for adjustment. If you have both valve covers off and set the flywheel to top dead center then one cylinder will have both rockers loose. This side, which ever it is, is at TDC. The other side is also at TDC but on the exhaust stroke. After setting one side spin the crank, with what ever method you use, 360* and it will be at TDC again only on the other cylinder. To say another way, when the bike is at TDC one side will be ready to adjust, this side should have loose rockers, both. The other side is 360* around.
I guess it may be possible to have a valve that tight. But I agree with Mr Bamboo it doesn't seem likely. That's why we think you adjusted the valves on the wrong side.
Moving right along. The other method of determining which side to set may be instructive. Take the valve cover off one side, I usually start on the left side. I use the Hex Key in the alternator bolt to rotate the engine and watch the window for the TDC mark and at the same time watch the valves, particularly the intake valve. Right after the intake closes is when the TDC for that side will appear. So I watch for the intake closing and as soon as it does I watch, it'll be pretty soon but not right away, the TDC mark. TDC. Then to find TDC on the right side I only have to rotate the crank 360*.
There should be very little to no vertical movement of the rockers. There will almost always be some valve tapping noise. And the clutch linkage in the trans also rattles in neutral. Just be thankful most of these motors don't have the Turkey Gobble Valve any more, most have been changed out by now. But if you get this thing running and you hear a Turkey Gobble noise when sitting at a stop light we have a fix for that too.