on the reverse thing... the 300 (vickers) is spec'd to be 3.9mph in reverse... the specs I read for the 1970 12hp soverign states "reverse... to 4 mph" I assume this to be at 3600 rpm going down hill... : ) just for comparison the 300 specs to 8.1 mph fwd... where the fwd speed is spec'd "... to 7mph"
im with Larry on this.. all the slop that develops in the linkages cause the movement at the hydro to decline... tighten 'er up and run reverse all the way to the ice cream stand... (or where ever!!)