[Lumps!] S II Dash Woes / Newbie returns

Hi All,
I introduced myself a few months ago, watched a while, un-subscribed from
ALL my lists, bought a lump & now I’m back on LUMPS.
I’ve just purchased a '79 SII XJ6L with a 4 bolt 350 TBI & 350 trans. It
also has an XJS limited slip diff with 2:88’s.
It came from Colorado, and aside from the rear valence under the bumper, is
virtually rust free.
Needs paint & interior & some TLC, but the engine runs strong & it has good
positive shifts.
I plan to make it presentable & use it fairly regularly, possibly replacing
my wife’s car [Yes Mr. Hagerty, I’ll change the insurance if that
My other toys are:
'62 E-type, restored then mini lumped with 105 amp Delco Alternator,
Nipondenso gear reduction starter, Mallory Optilite distributor, MSD
ignition, Aluminum radiator with modern cooling fan, & a couple of other
'64 MGB, not “restored”, but very heavily “maintained” and lumped with
electronic ignition & Delco alternator
'91 Miata, still original, but I understand I can supercharge it for
$2500…hmmm…or there’s the Ford 5 liter conversion…maybe the new
twincam 4.6???
'90 BMW 735 IL (mama’s car & unadultered)
'93 4wd GMC Suburban (works in the snow)

Now the question:
I have the dash out o the XJ6, because the rubber connectors between the
side vents & the main AC box have come loose. They seem to be in excellent
condition, just not connected.
I managed to get them reattached to the big plastic box behind the center of
the dash, but am having pure HE** getting the side dash vents to slip back
in their places.
If I take the rubber thing out of the car, It isn’t too big a deal getting
the dash vent to slip in to it, but I just can’t seem to manage it when
everything else is in place in the car.
Anybody got any tips?
Thanks. I’m sure there’ll be more later.
Jim Carney