I think on the JE pumps, to replace the bearing, the shaft has to come out the front. I'd definitely pull the bowl and check out the back side of the impeller, and condition of the bowl.
I at least try the CSM unit, however, it trims first, and steers second. Similar to a Berk Jet-o-vater. (Provides wonky steering) A Place diverter steers first and trims second.
A mild 460 should push it to the mid 50s. I'd keep an A impeller in it, which it probably has, given it was 455 powered previously. Definitely need to check it out. Logs and snails for having the kiddos around.
Hmmm, half stringers? Up to the back of the front seats? Need pics.
Oh, and welcome to scjb.
Dan'l