Okay, final tally, for anyone who wants to repeat. I make no warranty about the safety or suitability of this, nor am I recommending anyone do it, this is just an accounting of what I did.
Engine was upgraded from original 190cc Briggs 675e to a 344cc Briggs Intek 21R707-0079-F1. This engine is total overkill, but it's the only vertical shaft engine over 275cc that I found with on-board fuel tank and electric start, which would fit on this splitter. Only required mod's were drilling the new bolt pattern and swapping the lovejoy coupling for the new shaft diameter. Shaft length was the same as the OEM motor, so it mated right up to the stock pump mount.
Pump was upgraded from 11 GPM to 16 GPM... after all, that was the whole point of this exercise.
Line from valve to top of cylinder was upgraded from 1/2" OD hard line to 5/8" hydraulic hose with SAE-10 fittings. Part of this was updating the 1/2" NPT x SAE-8 elbows to SAE-10. Return line and fitting also upgraded, as already outlined above, in detail.
Finally, electric start was added. I found the larger pump created enough load on that big motor that it was pretty hard to pull over in warm weather, and I figured it would be just about impossible to start in cold weather. I spent a while thinking about how to add a starter battery (group U1) to the splitter, and finally realized I really don't need a battery. Instead, I'll start it off the tractor battery, since I always have the tractor with me when splitting. I made up a cord with a forklift style battery plug, to connect the splitter to the tractor. One advantage is that I had to add a key switch, which gives some level of safety, since the splitter sits outside.
I posted photos of pump and motor above, so these pictures just show the solenoid, key switch, and wiring for electric start. I need to order some grommets, so I can clean up the wiring a bit, but it's working as is.
Cord and tractor will be used for the first cold start. After that, warm re-starts are easy enough with the rip cord.
