I am in the same situation right now with my Giant Vac unit... just like yours. I ran a Lesco leaf loader for years prior to upgrading to a larger unit. The Lesco had a metal coupler that slid over the round part of the metal impeller cover and just pivoted and clicked/locked into place. The coupler stayed clamped to the leaf vac hose so you didn't have to tighten and loosen the clamp every time you go to move the loader.
I will try to find some pictures of the way its setup. Unfortunately my Lesco is stored away at the moment.
When I have some time I plan to weld up some metal to build a 12" coupler that snugly slides over the Giant Vac. Make to small " L " shape cuts out of the side that goes onto the vac. On the vac side of things ill drill two holes through the round part of the impeller cover and weld two bolts protruding from the inside out of it. This way the collar that I create can slide over and pivot into the " L " shape cut out.
Problem is finding the time to work on the leaf vac when its being used so frequently this time of the year.
Snyder's Lawn & Landscaping
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2009 Sure-Trac 22' HD Open Trailer
(3) 60" Exmark Lazer Z's
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(1) 36" Scag Walker
(1) 16HP Lesco Leaf Vac
(1) 6.5HP EZ Trench Bed Edger
Echo: SRM-261's, PB-755's, SHC-212, SHC-265, HC-160, PPT-260, CS-346...