Andy - What is wrong with the U/C? Remember - a HE does not really use the U/C all that much (and when it does, it's not really under too much load - unlike a dozer). So perhaps, even if it does not look great, it might last for a long time. The problem is that including parts & labor, U/C repairs can easily exceed the value of many older machines.
One quick thing - If the roller flanges are wearing on the link pin bosses, if you just cut down the flanges on the old rollers this will be "fixed". It worked on my old 977.
Other than that - look for used parts, off a machine that has been scrapped.
Good luck.