If your '91 has a cable throttle (running over the head) then it'll also have the heatshield, in which case you need the manifold that is drilled for the heatshield (drilling is on #4, on the 1&4 branch)
If you have the earlier solid rod throttle control, it'll have no heatshield.
Just one more thing to remember, as you have a classified up and running.....the S4 spider manifold is unique to S4 in that it is designed to clear the power steering box so make sure the PN is correct.
Yes, if you're replacing the manifold do the top and bottom gaskets at the same time. It would be false economy not to.
You can ask JoeCab at Centerline but I doubt they'll have that bracket. I found one to retrofit my '91 but it was from someone who was parting out a car. Alfa Parts Exchange *might* be able to dig one up, but Larry tends not to have "fiddle-farty" parts like that. Can't hurt to ask, though.
Your best bet would probably be to cut out a piece of cardboard to fit then cut it out of steel plate. You'll just need four longer bolts. It doesn't have to be perfect, just something to hold the manifolds together at the bottom to add strength.
Quest for the part is at an end: Centerline had a NOS 1-4 exhaust manifold as well as a complete set of gaskets and brand new brass nuts. They're on their way. Couldn't ask for more than that! I'll revisit this thread to report on the "cure's" effectivenes. Thanks, once again for everyone's help.