I bought a 2 into 1 from Hooker Headers when they were closing out all their motorcycle stuff (well their non-Harley stuff that is) and they turn up on Ebay every so often. I have heard that the 500T actually makes more power with individual pipes on each cylinder. I wonder if a later model CB450's header pipes would fit the CB500T? Then you could adapt some universal mufflers or maybe some Supertrapps?
If he does that it'll cost more than any reasonable person would pay. I've got two thoughts: One, if you don't like the 500T headers (they have that funny collector thingy), they're a direct swap for any of the 450 stuff including the CLs. My temptation would be to take 450 headers over to a muffler shop, have them put a 30' bend in the pipes about 6 inches back from the muffler and stick some shorty reverse cones on there. There you have it - cheap upswept cones.
I purchased 450 exhaust and can say they are not replacements for 500T. The end that attaches to the motor is a different design and a smaller diameter. The curvature is also slightly different and interferes with the back brake pedal.