Late to the party but here's my take on things.
Epoxy works best when there's lots of edges to hold onto. So coarsly scuffing up both surfaces will give a better bond. Also the areas will need to be totally degreased to a "T".
Having said this epoxy only forms a mechanical bond. Over time the use of oils, any cleaning solvents and warm water we use to wash away the BP residue will likely take its toll. So don't be surprised if the mount falls off some day. Especially since the primary load direction will be direct tension instead of shear.
Because of this and the fact that I'd want to only do such a job ONE time I'd likely go with either soldering or the dovetail.
Solder comes in a huge array of types from soft electronics solder that would not in any way harm the blueing up to silver brazing which requires a dull red hot heat to bond well and would obviously totally burn away any blueing. In between you'll find some manner of solder that has a good balance of strength and required heat. And likely it would hold a good fitting latch just fine and not result in any damage to the blueing around the latch. I'd trust a good solder far more than I'd trust an epoxy.
Finally there's the filed in dovetail option. There's a number of tricks you can do to do the job in ways that are just as good as a milling machine. It involves setting the barrel down between two supporting rails which act as file stops for cutting the depth of the dovetail. The stops, and some skill, will produce an accurate and flat base for the dovetail slot. The initial "hogging out" would be done using a square file. Then I'd cut the undercuts using a smaller triangle die sinker (straight sided instead of tapered) file that I put a safe edge onto one face. The safe edge would be down so the depth does not increase and I'd cut into the sides to produce the undercut while resting the safe edge against the depth stops. Along the way I'd check frequently and adjust cutting to the fore or back undercuts to shift the latch fore or aft as needed so it moves to a position that will mate up with the loading lever catch and comes out "just right".
Such "filing rests" were common fixtures way back when and something you'd find many of for doing various operations in any good machinist's shop. The design and use of such filing rests is identical to the stoning jigs used for doing various trigger jobs and such by gunsmiths. I like the idea of such a jig over the purely hand operation shown in the Midway video. For a one time use a jig of this sort doesn't even need to be anything all that fancy. A block of hardwood with a slot to hold the gun's barrel steady and that is clamped in a vise would do the job. Files cut wood so slow and poor that it would easily produce a "good enough" job on such a one off.
http://www.youtube.com/watch?v=W60yBwzipKA&playnext=1&list=PLC3AA68115468CF99