Hi vint-mow
I can only offer my thoughts here.

Tecumseh were the most astute of companies in two strategic moves:
They acquired Lauson 4-stroke designs; and Power Products 2-stroke designs
in the late 1950s.

These would form the basis of future Tecumseh engines.
I have read that Tecumseh chose to retain the Lauson name until the miid-1960s;
because it was an old, recognised name. After that, Tecumseh would remove Lauson designation.

I feel 'L' is more likely 'Lauson'.
After about 1963, we have simple VK designations: VK and HK engines.
These wre the vertical and horizontal Kirbys.
Later on, we would have Kirby Tecumsehs, with the brilliant Indian Chief logo.

https://www.outdoorking-forum.com.au/forum/ubbthreads.php/topics/66618/kirby-brochure-c1970s.html#Post66618

Quote
I was never sure of the reasoning behind their decision to swap the ports, but I suspect there was some technical rationale for it
I find it interesting - you comments on the development of this engine.
Maybe the port change was to move the exhaust away from the fuel tank?

Many thanks for your research here.

----------------------------
Jack