I'm glad you brought this question up. I've been meaning to make a post on it.
I've personally done four LIM gasket jobs now (three on my or my family'* cars, one helping a bud). Each time I did just what you say, "angle" in the LIM onto the elbow, then "rotate" it down onto the LIM gaskets. Of these four jobs, two wound up leaking from the elbow where it joins the LIM. I had to go back in and remove the tensioner to re-install the elbow, and that worked alot better.
From now on, I would personally recommend that the tensioner be removed during a LIM gasket job, because I found it alot easier to correctly install the elbow.
2004 Buick Lesabre Limited, Gran Touring; Bone Stock
1998 Buick Lesabre Limited, Gran Touring; Mods: Poly sway bushings/endlinks, Tru-Cool trans cooler, Thrasher shift kit (med), PLIM, front PEM; Mods in progress: Alot of stuff, but slowly...