Well, that seems right…But, you must remember that in order to change that shift rod, the gearcase must be disassembled….So, you may as well plan on resealing it while it is apart and replace the water pump impeller….

Well, there are a few ways to go about finding the parts. Looking for new NOS stuff, will probably be pretty expensive. You should probably start with confirming that your engine is a 1954 and obtaining the proper parts list. There are some differences between the spring mount mid section and the rubber mount mid section that was introduced in 1956. I’m sure the extension housings are the same, but not so sure about the upper driveshaft/water tube/shift rods. Once you have the proper parts list, we can determine if the parts are the same and what model year engines can provide the needed pieces.
I would look for used pieces, not too tough to find. It may be even more cost effective to find a whole donor engine to provide the needed pieces, perhaps a blown engine with a bad powerhead. It is a bit of a risk, the used upper driveshaft might be grooved excessively in the seal area, but you will probably obtain the whole engine at a pretty low price, worth the risk.
I would offer to keep my eyes open, but we first need to be sure the upper driveshafts/water tubes/shift rods are the same between the two different style midsections….