BURNZEE, I had the same problem that as I tightened the screws the lock got harder to operate when I installed a new L100 (also from Inland RV) in our '66 Overlander. I had to carefully play with the tightness of the screws to get the lock to work properly with the key, but yet still seem to be tightly installed. With some work you should be able to do the same. If you are concerned about anything loosening up, use some Locktite on the screws (although I didn't and it is still tight after one season of usage).
I should point out that I also had to inject some LockEase into the tumbler to get the lock to work smoothly with the key, even before I tightened the screws. It was very stiff as received from Inland RV. Anyway, after the LockEase and screw troque adjustments, our new lockset works fine.
And to 67wanderlust's question, the only item I had to modify to make the new L100 work on our '66 was the original gasket, which I trimmed slightly to reuse with the new lockset. Other than that it was a direct "bolt in". I think perhaps the plate mentioned is required to make some locksets fit later era (i.e. 70's) Airstreams. I can't imagine there being any difference in the installation of the L100 in a '67 vs. '66 Airstream.
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