Any ideas what these are for?

They could be pipe layer brackets. If the machine was a pipe layer it would probably have a non occilating equaliser bar, have a check to see what it looks like. if you dont want the brackets on the tractor i would cut them off and tidy her up. Does seem strange that the blade trunnions are welded on.
Regards Gordon.

That's what they look like to me aswell Gordon. That's the side the counterweights and drums are mounted on. That tractor has an equilizer bar but I wonder if the carrier roller support might bolt on where the hard bar once did. They might have used good frames from a pipelayer on that D7. If the support was in the right place all you would need to do is weld on diagonal braces.
Later Bob

hello bicicat ,are there the same brackets on the other side ? ,i could have been a farm tractor with ammonia tanks for cotton ,bruce oz

Mornin.... Seems strange having that trunnion welded there.
Bob i think even pipelayers need to have diagonal braces do they not ? Would you not still need suport for either the backend or trackframes ?
Regards Gordon.

Hello and thank you for your replies. the plates are identical on both sides of the tractor. The equaliser bar does swing but that could have been changed at some point. Could the plates welded to the chassis done the same job with maybe a linking piece bolted in?

Most of them don't have have a diagonal brace Gordon. They have a very strong hard bar across the frames and it's very close to the point of max load.
Later Bob

Yep we learn something new every day.....well i do anyway.Lol I remember a guy who bught an IH BTD 20 he did not know that it was an ex pipe layer fitted with a blade, a non tilting angle blade at that !!! i think some modifications had to be made after levelling proved to be a little awkward.
Regards Gordon.

We had trunnions like these on our 7E and 7F for a Holt root plow.