The wipe bezel is possibly "glued" in place by a 50 year old degraded rubber washer.
there is a number of ways of fixing the rusted up speedo fixings
easiet is to just fit a replacement, or transfer your internals into a better casing. There are lots of spares floating about, though most will be MPH speedos, so swapping casings is probably way to go.
you could also get some thin studdng, remove the damage done one, and fit a new stud, either gluing in or double nutting.
the length is important to get the straps at right angles, and you can not shorten the straps.
And try to keep the black accountants driven black plastic dash, most got changed to wood over the years, so not many cars still have them.