850 clutch shims & re alignment re visited

I recently put a request for info and advice about the above topic. Thanks for the info I got back. I still have a problem though with the alignment of the two sprockets namely methodology and accuracy which leaves me less than convinced or confident enough to start closing the primary case up and job done. With a straightedge I am finding it very difficult to get an accurate reading other than 'near enough is good enough'. I am pushing the straight edge against the engine sprocket as best I can just below the first row of teeth and trying to gauge by eye the run off against the clutch sprocket. I have tried with the inner case on and off but cannot see any obvious deviation over the distance. Whats also throwing me is that originally I had over a 100 thou in shims but with the gearbox rebuilt the readings I am getting now allow for about 30 thou is this possible. I'm trying to convince myself that what came off must go back on. Stupidly I did't take any pics of the back of the clutch basket to see what was there in the way of shims. When I came to re build I had three shims cable tied together in the primary drive box so assumed that this what was on there in the first place. Is it possible to have no shims at all behind the clutch basket?

I have all the clutch plates in and both sprockets 'nipped up' on the taper and shaft