A/C tensioner / belt

Yes, but in a little different form. On my ex-308-2V there were shims (maybe 8~10mm total thickness) added to decrease the crank-to-AC compressor distance to give more/some wrap on the AC idler pulley (but it's still a pretty marginal design IMO).

 

I've just been through this. I had two shims on each of the upper posts of the AC compressor and the belt was too tight. Not quite guitar string, but definitely too musical. I had a couple of shims made and the AC comp cam down just enough for the tensioner to take up a small amount of slack. If it is too tight, you'll kill the compressor bearings. The tension specs are in the WSM for new and used belts.

 

The downside is that without the idler pulley in place you'll increase the unsupported distance on the slack side of the belt, so depending on the runouts of the crank pulley and AC compressor pulley, the slack side could oscillate pretty wildly at certain RPMs (if the resonant frequency of the vibration for the extra length span is in band).
The SPCs actually show the nominal condition as "2 shims present" on each stud, and I wouldn't consider a missing AC idler pulley as a "plus" so why not add the shims and adjust as per design? IIRC the max shim amount gets limited by the stud length and keeping enough thread for the nuts on the top -- and I'd add the max shims to increase the wrap angle on the idler pulley -- JMOs.

 

I'm not sure about the 308 but my 328 is a Euro and the A/C belt is different. I'm sure that I could put a US belt on but it would be too tight. The Euro belt is slightly longer and a much better fit.

 

Walt -- Measure how far the threaded studs protrude above the 3 nuts on the top of the upper bracket (hanging off the camcover) -- that will be the "easy" max total shim size you can add. The "stock" shim is shown with a slit (like a camber adjustment shim), but thick washers would work OK too IMO.