Model H/M factory options

Did Farmall have a factory low speed option for the H/M tractor. Watched a nice looking H pull at full throttle at about 1.5 to 1.7 MPH on the computer operated display sign. I was told it came with a set of factory optional "Cultivator Gears" , in fact, there were two H"s at the show. The four cylinder engine sounded like a V8 when wound up. I know of several after market options for gearing but I think they increased the speed, not decreased.

There was a 1.5 mph low gear attachment available.

I have an original brochure, "The Farmall System of Farming," no date, but probably about 1942. I have somehow managed to keep it intact since I first took it off a dealer's info rack when I was a pre-teen.
The brochure quotes speeds at 1650 rpm full-load governed speed, on 10-38 rear tires: The "special low-low speed (pneumatic tires only) 1-5/8 m.p.h."

"Special fourth speed (pneumatic tires only), 7 m.p.h."
I don't have the no-load engine speed handy, but it might be around 1800 r.p.m., so the ground speeds would be proportionately higher if the tractor were not loaded down enough to bring the engine speed down to 1650 r.p.m.
This higher fourth speed would make the tractor a lot more useful for some jobs around the farm.
My father had two H's, both with the standard gearing. To pull a heavy load (hay, grain, corn) over a gravel road, you had to use fourth, which gave a little over 5 mph with the engine roaring full-blast. Fifth gear was useless in these conditions because the engine would be running at idle speed at 5 mph, and there was no torque to pull a heavy load (the IHC brochure quotes minimum speed in fifth gear as 9-1/2 mph, which means that the engine is running fast enough to give a little torque). The higher fourth gear would have given a nice "road gear" for the gravel roads. It would also have been useful for some field jobs, like pulling a spike-toothed harrow, with the engine maybe throttled back just a bit.
The H was/is a lovely tractor, pleasant to drive, comfortable (for its day, at least), reliable, fairly agile because it wasn't as big and clumsy as its predecessor, the F-20, BUT
the gearing was not as well-thought out as that of the JD and Oliver tractors, which had a fifth gear around 8 mph (VERY useful) and a "road gear" around 12 mph (plenty fast on gravel roads and on the trails through the fields).

I have a set of these low speed gears in my M. I have heard of it also called corn picker gear set. It also slows the reverse up too.

where could i get the low gear kit and what does it take to install?

Yes there were optional low speed gears. Serial number should end with X6.