JDP,
I'm no metalurgist but, I think grinding the primary bevels before heat treating would make the process and particularly the final sharpening far less labor intensive. (if it can be done like that).
Either way, you will save yourself a bit of sweat and aggrevation by making some type of fixture to hold the heads at a constant angle during the grinding process. This will also insure uniformity from bevel to bevel and broadhead to broadhead.
I'd like to point out that using a grinding wheel of any kind will produce a hollow-ground bevel geometry which, the good Doctor has found to be far less desirable/durable than a true flat grind. You could get a flat grind using the side of the wheel or a disc sander but, be aware that there are potential problems with this too.
On circular wheels/discs, the outer perimiter of the wheel is moving much faster than the center is. This will result in the end of the blade near the outside edge of the wheel being ground faster than the end near the center. You can overcome this problem by moving the broadhead across the wheel as you grind, you just don't want the head to climb onto, or drop off of the edge of the wheel. (instant divit)
I like belt sanders because they eliminate all the above difficulties. You'll still need a jig or fixture of some kind to hold the correct angle but using waterproof coarse grit silicon carbide or better yet zirconia belts (Mcmaster-Carr)allows you to set the bevel quickly without worry of overheating the blades because you can quench them frequently and not ruin the belts. I have found that aluminum oxide belts are pretty poor for metal stock removal.
Also whenever using power tools to sharpen any blade, be sure the tool's rotation is away from you so if the blade ever grabs, it will be thrown away from you not into your body. Hope this helps,
Ron