A couple suggestions.  I didn't change my thermostat on my '85 but tried to
change  the 3 inch hose between the thermostat housing and the engine, which
resulted in me having to remove the housing.
1.  Use plenty of penetrating oil on the bolts before trying to remove.  I
didn't and ended up stripping the heads and spent the rest of the afternoon
first trying to remove it myself, then going to machine shops, NAPA, and a
tire store to get their help.  thankfully, with heat, we were able to get
the bolt out.
2.  Since this section of hose may be the hardest to remove/replace, my
suggestion would be to remove and replace it at the same time.  I got the
hose from vanagain.com.