What dealership and distribution networks? Checker sold most of their cars through direct sales and were carried by only a handful of independent multiline dealers (when they first started selling non-taxi cars in the late 50’s, Checker would pay your way to Kalamazoo to pick up your car). And IHC mostly sold Scouts and Travelalls as sidelines at their heavy truck and farm equipment dealerships.
Also keep in mind that IHC was (still is) a huge company with a very small light truck division, whereas Checker was a pretty small company that pretty much exclusively made taxicabs. Would it really make that much sense for a company that mostly made tractors and combines to buy a company that made taxicabs? Certainly stranger mergers have happened, but I don’t think there was anything that would make such a merger inherently beneficial.
Checker just went bankrupt, though-- I think someone should buy the name for cheap and start making hybrid Checker-badged cabs.