Chris made a quick change holder and bolted it in. I think that will work good, certainly makes welding on the holder easier. Had we thought of that before I welded my holders to the press I think I'd used that method myself.
Here's what I did to hold dies in place. Just finished a bit ago and haven't cleaned it up yet. Still got to add a small chain to each pin so they don't get lost and to give something to pull pins from holes (nuts) that won't be so hot. All in hindsight I would have cut the "L" bracket longer so all it needed was to drill a hole and drop a pin in. The top holder is the same, but with short bolts used for pins. Those dies get HOT in use.