Mercury 3.9 hp Outboard Power Head Cylinder Block Crankcase ect  what you see .So 1964 was the first year of this family group .In 1969 it went to 4 HP and middle 70s 4.5 .They were great motors hard to kill but ?.This was a long shaft kicker don't think it saw salt , water, fresh water has a lot of hard minerals camera flash makes things look whiter .The spline pict is the D shaft from this motor .I saved it from the scraper because the ring seal is so good .A lot of motors loose the seal at slow speed like turning the fly wheel slow .A simple test for motors is see if you can pop your finger like a wine cork when you pull a vacuum or pressure around TDC ( leak down rate ) a good motors will hold that longer then one not so good or at all wore out or damaged .This motor has sat a round the shop for years turning the fly wheel over slow with the plug in - it fights like in a good way around TDC . An other trick is to put CLR or lime away in to the water passage to make sure they are clear .That trick works great on old uncle salty to, you don't have to pull the covers and if it was over heated the compression would suffer . Last I'm going to list it as ( local pick up ) . I can strip it down to the block or take it all shipping is a pain and the fly wheel weights a lot and you don't want it to get broken let me know and we can work on it I could pull the fly wheel and send it seperate its weight is close to the power head  .Its just the price of larger heavy things. If your trying to fix a 3.9 or 4 (point IGN ) this is correct vintage .  Thanks for looking and I don't knowingly sell  junk ( not worth it ). As I remember short shaft 3.9 were 56 LBS complete - sorry E bay made me put a weight on it (red writing ) .I tried to leave off I will work with you on shipping.