Yep, simplicity on a proper lister. The rod will go down the bore. Like all car engines (well almost all) ring clamp around the piston, slide piston down with help from a hammer handle (wooden) leaving the copmpreesor on top of the block and job is done. A single size clamp can be made for say 4 1/2 inch piston but the commercial ones are the expanding type for a range of piston sizes.
As several have mentioned elsewhere, protect the conrod bolt threads so they can not 'ding' the crank, if the rod gets skewed, and torque it up from below. Much less hassle, no interferernce with the gaskets under the cylinder block, much less lifting effort. All ways around, just plain easier and simpler.
Ring expanders do the other job of enlarging the ring in a controlled manner for slipping over the piston and easily into the right groove, or for easy removal.
Just looked on Draper Tools site - cost 8-12 quid for an expander and 4.30 for the pliers (+ shipping).
You have to remember that these engines were derived from stationary engines with cylinder and combustion chamber cast in one piece (no separate cylinder head), so piston had to go in from the bottom and assembly methods were limited. It was a common, well known method and was carried over into the diesel engine (from the small petrol side valve engines) 'cos that was the way it was done and was simple enough with a minimum of tools required (and nothing specialised in any way). Spanners, hammer and screwdriver were probably all the tools needed/used for most maintenance. Oh, and a scaper tool for scraping in the bearings.
Regards, RAB