I have guys trying to jeer me with this same thing when I drive my '24 T and '29 A to the pump.
There is absolutely NO reason justifying the use of leaded gasoline in an industrial engine, the Allis included... and pre WW2 engines don't need it, either.
The only engines subject to valve problems from LACK of lead, are low-quality non-industrial engines that have plain (raw iron... no insert) valve seats... typically, they're between 1949 and 1970, and automotive.
Realize... TetraEthyl Lead (TEL) wasn't introduced to domestic (non-military) markets in any significant volume until AFTER WW2.
Manufacturers (Especially Ford) found that, with TEL being a pretty much 'standard' fuel after WW2, they could save manufacturing cost by using cheaper valves and omitting hardened inserts from their postwar flathead V8, and other engines. As a result of wartime aircraft and marine engine development, manufacturers also recognized that they could get 'more free power' out of a generally poor engine design simply by advancing the ignition... as long as preignition didn't occur. TEL would reduce that, so a manufacturer could boast another 10-15hp from the same engine, simply by specifying 'high-test leaded fuel', and advising that if one didn't they'd simply have to retard the ignition.
Did all engines prior to WW2 have hardened seats? Of course not... PRIOR to WW2, casual valve jobs (grinding, lapping, and adjustments in automotive engines every 12,000 miles were considered commonplace, so it wasn't a surprising thing... 12,000miles THEN, was viewed as a whole lot more than what we see NOW...
But in an agricultural or industrial setting, the load is significantly higher, which means higher running temperatures, higher stresses... hotter valves and head castings. In this circumstance, things like hardened seats and sodium filled valves were necessary, lest high maintenance and significant failure rates would cause farmers to abandon your product simply because it wouldn't last long under the agri/industrial duty cycle that automotive applications simply didn't require.
Now, to take it a step further, realize that TEL was not only unavailable before the end of WW2, industrial and agricultural engines PRIOR to WW2, and WELL AFTER, ran on plenty of other fuel types that had no TEL. Propane, natural gas (stationary power units), generated methane (digester gas), Distillate fuels... None had TEL. From the start, there was no provision for, thus no need intended... for lead.
So the answer is no- don't waste resources thinking it 'needs' lead.
Now that said... for flathead engines, running a little Marvel Mystery Oil in the fuel every so often does help clean tarry goo off the valve stems... but just on flatheads. Due to the poor flow and thermal problems inherent to the flathead design, carbon soot mixes with unburned fuel and a little oil loss, to accumulate on the stems and the valves start to stick. MMO cleans that crud out pretty well.
Zinc in the oil helps provide lubrication to flat tappets and cam lobes. The unfortunate removal of zinc from motor oils results in the classic flat design winding up abraded to heck pretty quick... so gotta have zinc. I converted three of my boat engines to roller-hydraulic lifters specifically to combat that issue, and I've rebuilt two others after the owners did oil changes WITHOUT realizing the new oil was insufficient for their flat tappet camshafts.
------------- Ten Amendments, Ten Commandments, and one Golden Rule solve most every problem. Citrus hand-cleaner with Pumice does the rest.
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