Ayuh,.... I donno,... If it's all original, Yes,... probably oughta be askin' in the Merc I/O forum though, or the Non-repair I/O forum,.....
The 4.3l usually runs a 1.65:1 or a 1.84:1,....
If ya got it off the boat, just turn the drive shaft, 'n count the prop rotations,....