I bet you could cobble together your own conversion kit with a handful of 1" ITW split-bar no-sew buckles (aka, "field repair" buckles). These are compatible with the buckles Mystery Ranch used on their pre-Guide Light MT frames/packs.
ITW 1" Repair Buckle (SRB) consisting of 2 parts to make 1 unit:810-1064-xxxx – SR 1” female replacement buckle810-1058-xxxx – GTSR-1 male The main design goal for these buckles was to replace broken 1" Side Release Buckles (SRB) without any sewing required. They work great for that, however I...
A handy split-bar buckle part to allow more repair style buckle options. Great for replacing pack hardware and adding buckles to PALS webbing. These parts can interface with other 1" Duraflex Military buckle parts too. Note: This product is just for the male side and fixed slot / non adjustable...