Speaking of the agitator....
Though consumers probably weren't aware, the 1966-1981 WP large capacity machine underwent three dimensional variations that altered mechanical components significantly during their production run.
The first version, 1966ish-1973 was built to the same scale as the standard tub model, with the agitator shift rising similarly out the lid well of the machine. This first version had a four inch (or so) longer agitator shaft, special centerpost length, and therefore a custom spin tube. There is a huge distance between upper and lower bearings in these machines, and they are known for loud operation when worn.
In 1974 the machine was re-designed to use the same transmission and agitator shaft as the standard, and thus the agitators were re-designed and shortened. WP's answer to this was to use the standard Surgilator. Kenmore debuted the Pentas - the Vane and Swirl. These agitators require separate extensions to be added in order to accomodate a fabric softener dispenser. When this change was made, ALL belt-drives in production used the same transmission - the portable, the 24-inch models, and all 29-inch machines. I think that's pretty cool...
In 1978, the centerpost and spin-tubes were shortened five inches (a modification which is both great and awful in my opinion). Agitators didn't change nor did the view externally of the basket/agitator, but basket drives and spin tubes are different between the models. I like this modification because seldom if ever do we come across 1978 and newer machines that have worn bearings. The bearing roar/clack of worn bearings is not heard in these machines and WP finally solved the bearing issue that eventually can be the death knell for older BDs. BUT, this same short centerpost is also highly dependent on good center seals, which when failing or failed can cause large amounts of water dumpage into the bearings and down onto and into the transmission. The older machines can do the same thing, but it takes longer for the seals to fail miserably enough to flood these machines from all the way up the centerpost, thus the machines often lived longer. Cleaning up and repairing a gooey, flooded centerpost machine is not a fun job.
MickeyD - you CAN use a winged Surgilator in your machine should you ever want to do so. It would transplant/fit perfectly and might make for an interesting comparison of one 'tater versus the other.
Gordon