I was thinking one of the VexPro VersaPulleys and something something the slice in the middle, but the keying makes that difficult. You could get a 2mm deep slot on either by taking off the teeth. On the 42 tooth, you can only get 3mm deep if you go down to the keying pins, it’s up to 4.5mm deep on the 80 tooth.
We just got a box of these from McMaster today, when we get them working I’ll post a review of how well they worked.
The chain attachment points work great. Very sturdy and no problem holding the weight of 5 totes.
If you want to prototype a hook method - there’s the rubbermaid fasttrack (and some other equivalent) that the hooks fit inside the lips on the short side: http://www.rubbermaid.com/Category/Pages/SubCategoryLanding.aspx?CatName=GarageOrganization&SubCatId=FastTrackGarageOrganizationSystem
Also, if you don’t want to spend the money on the roller chain with tabs, you can stick an 8-32 bolt through the roller chain to transfer motion. You’ll want to obviously do a few to reduce the stress on any one bolt: http://www.buildblitz.com/linear-elevator-concept/
I’d be curious to see a picture of the setup and general geometry you used. Our current stacking design is planned to grab each tote individually, so will not see nearly as much load on each hook, but it’s interesting to hear that you can pick up 5 with the lip of just one tote.
What was the other prototype if you don’t mind me asking?