Most manufacturers sell replacement parts. What you propose MAY work, but I've never been a fan of installing something dicey that the next person may not be hip on how to avoid.
I can't find the IC rated at that price, not even close. I've been in to look, also, on their website at $15 those are not IC compatible, maybe I have t look harder at another store.I would recommend using new IC rated cans. They are rated for insulation contact and will not start a fire. You can get the cans from Home Depot for $7.50 ea. if you look around. Trims are about $8.00.
The original metal frame probably kept the can itself some minimum distance from the nearest stud.
I would say nothing wrong with using the old cans provided you maintain all of the appropriate clearnces, although it may be a lot of time and effort doing jury-rigging. I have seen square perforated metal "pipe", a small section of which could be used as a spacer through which a 2-1/2 or 3 inch screw could hold the can, minus its original frame, on a stud.
I have dong this kind of jur-rigging myself, including removing the factory supplied framing so the (brand new) can or other device would fit in the space provided.