M670 super PTO brake

My name is Walter. I'm in RI but last week visited my Brother Steve in Missouri. He has a '67 Minniapolis-Moline M670 Super that he bought approx. 8 years ago. It was in boxes and had the pistons frozen in the cylinders when he brought it home, and he has slowly repaired it over the years. It is now a working tracktor on his 40 achers (sp). The problem we worked on last week was the PTO brake. We had the case open to adjust the PTO clutches. They were slipping when he was bush-hogging tall grass. We got that fixed. While we were in there we found that the PTO brake band was broken off. This allowed the PTO to spin even if it was disengaged. This is a dangerous thing with several small children in the household. We bought a new brake band and installed it. However it still does not work correctly. The linkage (inside the case on the left as you stand at the rear of the tractor) only pulls up the brake band approx. 1/8 th of an inch when the cluth is disengaged. Hardly enough to pull the band up snug on the drum. The PTO shaft will stop at times when it is disengaged and a drag is applied. ie: bushhog is still attached. If we tighten up the band any more it will rub on the cluth drum all the time and wear itself out.
My thery is that the linkage has been modified. There are several welds that do not look factory.
We have the operators manual but it does not have a complete picture of the linkage. Does anyone have any ideas or possibly a picture of the linkage involved.
I had a great time working on this with my brother. I had not ever visited his home ( almost 20 years) and it seems these old machines have a way of bringing families together.

Thanks Walter

There is an auction this week with a MM670 Super Diesel with a WorkMaster #800 loader advertise. I would appreciate any feed back on what type of tractors those 670 are and some of the problems to look for (have read in a few post to watch for a cracked head, what would be the signs for that type of engine trouble) .

Thanks
Paschal