Here is a short video highlighting a Petzl Basic (generation 1) and ISC Fixed Plate Pulley combo that's been bolted together using a stainless steel carriage...
i've looked around, and i cannot find the xact piece of gear you're using that's attached to your saddle bridge. itz obviously some kind of an 'up-lock' device, as you are hanging there peacefully before you even attach your 'homegrown' contraption. but that homegrown thing is pretty cool. good job on that. i have both those pieces. al i'm missing is the carriage bolt. maybe i'll try it sometime