FAB = Filtered Air Box. Personally, it was my preference to have the exhaust on the engine when I mounted the cowl because you can't adjust the exhaust position (except the final run). But it's probably safe to do the cowl without; it's not even close to interfering unless something is terribly wrong. The FAB, as you can find on other threads, can be adjusted for better fit in the cowl. Basically, I followed the advice from Firewall Forward that said to start fitting the major, hard-to-relocate stuff first and then fit other stuff around it. So, exhaust, alternator, starter, cowl, baffles, FAB, ignition, oil and fuel lines, sensors, etc. in generally that order. Prop and spinner very last. Some things are easier to fit if you remove other things; I had to remove the exhaust to fit the FAB and I had to remove parts of the exhaust while running the starter cables and CHT probes. The oil cooler and lines had to come out while routing wires behind the engine but was kept handy to make sure nothing interfered while I did those routings. But it sounds worse than it really is; the engine stuff was much easier to work on, if more complicated than a lot of the riveting I had to do for the structure.
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