I set my brass cases up with central anvils for the caps, although I don't really think it's necessary.
For the firing pins, I use a tiny bit of thick crazy glue and set it with accelerator. Just enough to hold the pins while I finish loading the cases.
I think the tamped-down blackpowder does a good job of holding things together in there once all's done.
oh, and yes, I just slip the caps in there with long tweezers. nothing to it.
So rim thickness--
does this rifle need thin skinny little rims or will modern hull rim thickness work?
--Tinker