Two things...

Royal engines were built on the Pacific Rim for Royal Products, Denver, CO, as I recall, . They may have been an early example of "Rim Clones" - not forgetting the Thunder Tiger engines of similar source. The Royal engines may also have differed from their 'inspiration' engines - the OS of the time - in how the carb or venturi was mounted. If I recall, a drawbar locking the drop-in carb or venturi, a la ST, instead of the set-screws usual to the OS...

Second, one of the things I try to check when 'doing' an engine is that the rod is straight. Careful measurement of snug fitting drill rod through the big and small ends of the rod can indicate whether their bearing surfaces are parallel, and if not, can serve as tools to bring them parallel. If the rod is obviously bent, and that compromises working alignment and clearance, I don't have any suggestions other than to try to find a straight rod. (...and check that the bearing surfaces in it ARE parallel...)

The were attractive and nicely done engines. When Royal Products went out (in the early/mid 1980's?), so did all their engines, etc.

If you can straighten, or replace, the suspect rod, you should get good service from yours...

Luck!