These were the years of change at Fords.
The whole tractor and tractor engine production line was shut down and cleared from the factory at the end of 1964 and was move to Ebro in Spain . Dagenham became a purely car production plant and Basildon was producing the "X" series from 1964. As far as I know, industrial engines were tractor based and made on the same line as the tractor engines.
A Ford dealer at Potters Bar started to bring complete engines into the country as replacements/new engines, but Ford was not happy. Ford used blocks from Ebro to satisfy spare parts demand as the Super Major worked out its life. It is possible that this engine is one of those that came from Perrys, with a 1966 date stamp. Some of the best quality E1A engine spares come from Spain today.
The pump is not a Minimec, it is the older style pump with an industrial governor mounted in the housing at the back. The industrial pump is a different shape and size. The Minimec has a smaller and differently shaped side cover.
This is the "GM" mecanical governor from 1959 which looks more like yours.
You are right that the "FL" head started in 1962 so that should mean it is a late engine.
On an "agricultural" spec engine, there is a breather on the timing cover at the front and a pipe from the valve cover to the aircleaner. This pipe is not on your engine but you can see a shaped area on the valve cover where it is normally drilled and welded. The fact that you have no breather or pipe is not important, it is just a different spec. your breather is from the tappet cover behind the pump.
On a tractor, the sump forms part of the load bearing frame. It is made of cast steel and has a fitting for the axle support frame, (or "A" frame/wishbone) as part of its structure. You have a straight alumiumum pan which just holds oil on your engine.
The starter is an industrial/truck type pre-engaged by solenoid type whereas the tractor starter was pre-engaged by a hand lever which then switched the solenoid. In the application it was used in this would possibly have been operated by a key start switch.
These engines found their way into many applications with many manufacturers and, as a welder requires a constant speed and the "GM" pump operates at one of three speed ranges, 500 to 1500 rpm, 500 to 1800 rpm and 500 to 2500 rpm it is possible that the welder manufacturer found one of these more suitable and used the earlier pump. Combine harvesters with Ford engines came with the same governers.