Thanks Paul and Kirk for your input. I'll try the vinegar to reduce
the shininess of the replacement parts for now... although that's low
priority compared to getting the mounting hinge taken care of.

Quoting Paul Gardner :

> I really wish you luck if finding those parts. I haven't really been
> looking but I too have noticed a few of these mounting plates broken which
> suggest they belong to that "rare and expensive" category of parts.

The mprime site has a link for CS Machinery with parts for sale, and
Bill Kerfoot responded promptly when I pinged him at
csmachinery@z... I don't yet have first hand experience with
the quality of his parts at this point so this isn't an endorsement
but rather information that a source for Emmert parts is still
available. (I was uncertain because the webpage copyright date was so
old and life on the 'net is fleeting) He says he can provide the
mounting hinge, dogs, and the flat bar style tilt lock assembly, as
well as parts for the K style vises and a few others. I'm fortunate
enough that I have the tilt bench bracket and think my hacked tilt
lock handle will work for now. I think I'll try my hand at fabricating
the mounting hinge and order some dogs from him when the vise is
up and running. I may end up ordering the hinge as well, depending on
how my fabrication efforts go, but it's good to know there is a source
for the thing. He also recommends the flat bar tilt mechanism over the  
round rod so I'll see how mine works and consider purchasing a  
replacement if it's a PITA.

> I'm not sure how much metalworking equipment you have in your shop but I'd go
> down the fabrication road and make a new one.  You have a great template
> right in front of you. The raw material would be relatively easy to find.

I am fortunate to have enough of the original mount hinge as a  
pattern, and I have both 1/2" hinge pins too. I picked up a cut-off  
scrap of 3"x3"x1/4" angle and some scraps of 3/4" and 1/2" bar stock  
at my metal supplier on Friday.

> For the main bracket, if you have a metal bandsaw the shaping is really
> straight forward but you could also get by with a hacksaw, a grinder with
> cutting disc, a couple files, and a drill press.  For the hinge portion,
> the shaping is also fairly straight forward but maybe a bit more of a
> slog.  If I were doing it, I'd drill and tap both knuckles in addition to
> welding them to the main plate - but I'm a belt and suspenders type of
> person in this regard.

I don't have as much metalworking gear as I would like, but I've got
the options of cutting with my torch, tailed reciprocating saw, or
grinder. I like the "belt and suspenders" idea of screwing the
knuckles in place. That's a great suggestion, but I like it mostly as
clamp to hold the knuckles while I drill them. I worry about keeping
the bores aligned with the bore in the hub so I was trying to think of
a way to clamp them while using the hub bore to align my drill, and then
reproduce the orientation prior to welding. Screwing the knuckles in
place will allow me to attach one at a time while drilling the holes,
and also to check the final fit/alignment before committing my work to
the welder. My welder is pretty lightweight and will not give me good
penetration on this thick steel but if I chamfer the parts and lay in
multiple beads I think it will be more than strong enough, and then
I'll weld in the screw hole for added insurance.

> A cheaper and more available solution you'd want to
> experiment with first would be to lay a sheet of coarse emery cloth grit
> side down on the steel and beat the cloth backing with a hammer. The idea
> is that this imparts the pattern of the grit onto the surface of the steel
> leaving a rough finish that you can burnish via you preferred method (i.e.
> steel wool).  I'd then heat the thing up till it goes dark blue and quench
> it it some motor oil to darken the color.

Cool idea on using the emery cloth to simulate the grain of a casting,
although I don't think I'll be that anal-retentive. While I prefer
original parts/patina/rust/decrepitude, I still place function over
appearance and the hinge can stand out as a replacement. I may take
the advice on the heat/oil quench to darken it, or it may get paint.

Thanks again for the feedback. I'll post back with the results and
document the process if it turns out satisfactorily.

Paul, rust junkie on shores of the Great Salt Lake
SLC, Utah, USA