Hey Bryan,
Thanks for the update.
Questions:
1) Did you clean/tighten the "S" wire terminal on the starter solenoid? That, the fuse there, and the panel switches are the most prone to starting issues. There is a fix for the terminal at the solenoid, but it requires some soldering (eazy peazy.)
2) Do you preheat and start thru the key switch, or do you have preheat and start push buttons? Catalina installed panels with basically 3 different glow/start methods - not sure one(s?) were on the 34.
2) What is your purpose of, or want to accomplish by, or issue trying to overcome via, installing the solenoid?
Please understand that it does nothing to help you start "better". Its sole purpose is to cut the preheat time down from, say, 30-45 seconds, to 10-15 seconds. Then you sit at the dock (for what 10? minutes) warming up the engine, readying lines, stocking the beer, etc.
So yes, the preheat mod is great -- it cuts the time to shove off from a
highly unmanageable 10.75 minutes down to a
much more palatable 10.12 minutes. Meanwhile, you've added additional unnecessary failure points in the starting system, more terminal corrosion points, the need to carry a spare solenoid (just in case.) Better yet, you will be delivering full voltage (13+ volts) to glow plugs that are rated for 10 volts. And if you are out and say the battery remaining is very marginal, it wastes starting capacity activating a switch (solenoid) that is rated to handle say, 250 amps. The glow plugs pull a whopping 18 amps thru that solenoid. No, it isn't a ton of energy waste and probably won't make a difference, but does that make sense when it's a totally unnecessary "appendage" in the first place? If that 0.63 seconds "savings" is that important to offset the added cost, complexity, and failure points, we should all simply buy turn-the-key-and-go powerboats (but then we'd be sitting there waiting for the engine blower

.)
IF YOU do the mod (YBYC), there is
ABSOLUTELY no reason to use #8 wire. At 18 amps, #10 awg increases the V loss from about 0.02 v (w/ #8 awg) to about 0.04 volts. Really? Remember that's going to glow plugs that the mod is already over voltage-ing.
IF YOU DO the mod (YBYC), see my note on the TechWiki (right after the description of the solenoid mod) about using a 40-amp headlight relay instead of a 250-amp starter solenoid. They are <$10 at any auto parts (think of the cost of a spare) and it plugs into a standard wired socket, so all you do is pull one out, push the other in to replace it.
Bottom line, I've soapboxed about this mod so many times -- (ITSHO) it is one of the worst ones devised, and it's unfortunate that it's caught on "so well." It is not a magic bullet to improve poor starting, and masks actually correcting poor wiring. There are many more upgrades that will actually go toward eliminating poor-starts or no-starts ("starting" (ugh

) with replacing panel switches as you are doing.) Another is running a 10 awg "S wire" (if yours is lighter) from the start switch to the starter solenoid. THERE'S where you need full voltage. Some harnesses had 16 awg "S wire." If you did the ammeter to voltmeter switch, there's a 10 awg conductor (orange) sitting there waiting to be used.
Thud (stepping down from the soapbox)
-Ken