So I have a 1978 cb750k. I bought these exhaust pipes off ebay a few years back from a guy selling them as 1973 cb750K pipes. He told me that they were actually from a later year cb750k sohc and that they'd fit my bike. I think he said they were off of a 77-78. At the time I believed him because the top of the headers (where they fit into the engine's exhaust ports) looked legit. However. Trying to get these on my bike has been a pain in the dick. The headers fit on no problem with the flanges and crowns. But I cannot for the life of me figure out how the mufflers are supposed to go on and slide onto the end of the headers.
I've seen other pictures of these that look almost identical (4 into 2 megaphone pipes) the mounting tabs are all the same and it just won't go that way on my bike. Theres like a downward angle and no modified bracket can remedy that. Here are some pictures so you guys can see what I'm talking about:


On that first image you can see that downward slope on those mufflers. I've tried flipping the mufflers upside down and awkwardly mounting them that way and its just still no good. Any ideas?