Dave, get a caliper from any hardware store and measure the OD of the stern tube. I called Hunter myself for my 466 and it turns out they used 2 different sizes on my model with a 1/8" difference. It saved me from buying the wrong size which was actually in my manual. The caliper was $10 and well worth it. Taking the flange of is the big problem when installing the Shaft seat. Use bolts with a socket between the shaft and the tranny flange but be careful not to over tighten. Spray some liquid wrench or equivalent in first and let it sit a day or so. Make sure to clean the shaft well before installing. PSS instructions are fool proof. I did one on my Catalina 34 and this was my 2nd on the H466.
If you run into any specific problems / questions feel free to ask.
Good luck,
Chris
