Inside one of the many boxes I have pulled from my attic I found a deck in unused condition, but open. It consists of 26 8c cards, one of which has a small magnet glued to the back and 26 “random” cards. They boast the standard rider back design so I imagine this was a privately constructed deck. The cards are standard stock, no roughing and the 8c cards are not short or shaved in any way. Does anyone remember this setup and the routine associated? Clearly this is an 8c force with some sort of pk production maybe?

I think it is exactly what you said. I'm not confident it is a mass-produced deck, but hey I could be wrong. Possibly used for a self-cutting effect, although I'm not sure it would be strong enough.

I believe this is a 50/50 force deck used for rising card via a TT with something very attractive inside of it.