The orange corn heads could be adapted, my F corn heads and grain heads would also fit a G. (Older heads were not adaptable, the top hooks need to bolt on, have 2 spots to bolt the hooks on....)
However, Gleaner was very poor at getting any type of universal header mount, nearly every series was different.
If you went from a K to an F to a L as you grew your farm, you had to trade the whole combine and all heads for the new package.
With a JD, once they got their quick change throat worked out, you could keep your heads, just trade combines, and save some money. Trade the head a year or 3 later when you upgraded the planter.
I think that hurt Gleaner sales a lot. Who can afford to buy a new planter, new combine, and new heads to match all in the same year.
And your selection of heads is a lot smaller, because a different set for each model or maybe 2 models.
Poor planning there, one f the few things I don't like about Gleaner.