Robert, you can hold bolsters on with pins of the same material and then peen the ends of the pins into flairs in the ends of the holes that you made with the next size or two larger bit that you made the holes with. Another way is to use a contrasting pin or even a mosaic pin and put it in a straight, unflaired holes. A good epoxy between the bolster and the tang will also help with the fit.
Actually, I'm making a guard right now out of historic RR spike steel. The section of decommissioned track where I found it dated back to the 1870's, but of course there's no real way to date the spike. I've got a previous customer that has a piece of small ore car rail found in a mine in Colorado from a similar date and he wants me to incorporate that into a guard too. I kind of like using these steels that have a story behind them.