Heavy Duty or Standard experience

[Swivelhart]

I have a 66 OMC. The Larson archives for 1966 show my exact boat and the options for that were what they called the (high performance OMC) or the (heavy duty OMC). Looking at my parts manual for that year It is clear that I have what is called the standard group outdrive not the heavy duty. It seems most people who have these old OMC's have the heavy duty but has anyone had much experience with the standard. There are notable differences the most obvious being the waterpump driveshaft that extends all the way to the lower unit and is one piece (see picture). The splines on the shaft are only four big ones as opposed to the the many smaller splines on the heavy duty water pump shafts. Also the Lower unit is a two piece deal as in the picture.

Here is the two piece lower unit that sits below the exaust housing