I've found an effective way to tension the poly-V belt that drives the alternator that I'm posting here as a search hadn't yielded anything in this regard.

It is basically a bolt and long nut that I put as pictured and then loosen the nut while holding the bolt head (another nut in my case for lack of a bolt) to prevent it from turning.
This will increase push the alternator up thus tensioning the belt.
Tighten the nut and bolt on the adjuster as well as the two pivoting bolts and nuts, remove the 'adjuster ram' and go for a test drive.
When happy with the tension (no squeal after a cold start when driving off and accelerating up to 2k rpm) put the airbox back.