I think I've got it now, as close as it's gonna get. It's on the right tooth, but in the span of adjustment of the distributor, the closest I can get it (with the terminal grounded) is about 8 or 10 BTDC, which jumps to 20-25 when the terminal is disconnected from ground. The cam timing is spot on, but I'm thinking that after the heads and block were machined, everything ended up a tad off. To get the timing to 5* BTDC with the wire grounded, I'd have to machine the slot in the distributor a bit, to allow a little more adjustment.
That might be next.

Thanks for the help!