Having two lifters not pump up is certainly suspicious. The reason I ask about the cylinder location is that I might be worried about a blockage in the lifter oiling gallery. FE blocks have a lifter gallery that is fed from the back and runs to the front. I assume the Shelby block is the same even though the mains are a "priority oiling" system. Anyway, if the problem was in one of the two front cylinders, 1 or 5, then I would be suspicious of trash in an
oil passage. But, if it was one of the middle cylinders, then a blockage in the gallery would *probably* prevent proper lifter function in all cylinders forward of the problem. Not sure, but that seems likely. If the lifters forward of your problem cylinder seem to be working, then I'd guess that the
oil passages are ok. Still, two lifters not pumping up is odd. The problem I've always had with hydraulic rollers is them not bleeding down.
As far as taking them apart, you rightly state that you need to remove the tie-bar rivet. It's worth the effort if you're at all curious.
I think it's time to pull the motor, sorry to say. I feel for you. Interior, trans tunnel, and that stupid riveted panel under the dash...it sucks.
If you pull the trans with the engine (that's my preference), don't forget to track down one of those rubber shipping plugs that fits in the output of the TKO...you don't need trans fluid everywhere, adding injury to insult.
Chin up, this is the fun part of owning a cobra
