No, you can't just add the other tab. The original 67 tab is roughly in the center of the later two tabs and had a tapered hole for the tapered stud of the idler.
Jim, if someone was talented enough, couldn't they cut the old tab and weld two new ones in? I thought I'd read somewhere about people converting to the better idler system.
I just took the easy route and replaced the whole K member but I was also getting rid of a slant 6 K member and Schumaker mounts at the same time.