Yes the straps must be parallel when all bolted up.
One reason is when you change down then let the clutch up, the straps are in compression. If they are on an angle they will bend and flex, causing shudder.
Using washers is not a great way of setting the strap height, a set of 3 spacers made the correct thickness (whatever was faced off the flywheel, usually .200") is the correct way to do it.
It sounds to me like maybe the flywheel and backplate have been faced many times, without the lug heights checked on assembly.
To answer both your questions, read this article on how to set a Mini clutch up. It is important that it is done correctly.
http://www.minimania.com/web/DisplayID/ ... ticleV.cfm
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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.
