Is the currect RWP a gear type?

Not sure if you received my response.

Yes, two gears. runs off the back of the generator but I guess you know that if you own a 1954 Atom....

I was using water pump grease. After  a two hour ride it started to run hot. 

I presently have a 5/8" ID hose from the thru hull to the pump. I'm thinking maybe it should be larger.

Thoughts?

Sounds like somethings binding up if it's running hot. Open it up and check the shafts and bushings. Also, how tight have you got the shaft packing? Too tight will cause heat. Just like the prop shaft, you should get a very small amount of water seepage. The gease cups are for priming the pump only. The grease fills the gaps between the gears to create the suction. Once water is in the pump and if the gears aren't badly worn, it should pump water. No, a 5/8" hose is fine. Yes, you can go rubber impeller but a new pump with mounting modifications will be needed. 

I'm surprised you still have a gear pump on a 55 engine. Most were gone by the late 40's and rubber impeller were used. Is the engine the original? 

I will loosen the packing nut as it is not drippings now.

Thanks

Still trying to figure out how to add photos. I'm looking forward to posting Pics of the recent restoration.