Thanks all!
Hey hey! Well, oddly enough I ended up making a new friend here in Chicagoland who I think may have once been a member here under the handle Hoover1060. He told me about an adaptation I can do to make the 4109 kit work ("you just need a belt in the converter track to trip the speed switch")...and he says it'll have improved suction over the 1031 even, "because it covers the brush roll, whereas the rear conversion set leaves the brush open which loses some suction." Anyone have thoughts about this? I'm mostly happy because it means I get to use the hoses I have and not search for the more elusive 1031s on eBay.
I'm a mechanical idiot, so I think he's actually going to walk me through the process in person. I'm going to see him on October 30th when I pick up a vintage Kenmore 900 washer-dryer set in coppertone with those awesome console lights (I'm so excited)! That'll make our home 100% vintage appliances (except HVAC and hot water heater of course)!