Log tube OD should be 1-3/4". Performance Yachts (425) 355-3669 p/n 01-034-134 is a PSS std 3/4 log 1 3/4 should fit.

My coupling was rusted solid too. Had to cut the shaft out ($$). Replaced coupling with a split-coupling: std flange bolts to the tranny and has a split hub with two bolts that sinch down on the shaft, with keyway and lock screw. I'm told it will never rust solid because you can always pry the split hub slightly to pop the shaft loose.