From what can be seen I think your intuition is correct, they are press fit
bearing races. If so then it is unlikely you will be able to 'modernize' the
BB, as newer BB assume a standard diameter threaded housing. If the
shell is standard size, it could in theory be tap threaded. The Sheldon
Brown site has standard sizes listed, but an ID slightly under 1.37" and
a width of 68-73mm encompasses contemporary BB sizes, soon to change
however. ("slightly" meaning at most 0.02" under 1.37, and some reaming
may be needed)
If the races are ok, or only a little pitted, best to just reassemble after
cleaning, with appropriate masking of the BB area in powder coating. From
the amount of grease and the bike frame configuration it is unlikely the
bike has gone more than 100mi in its entire life so wear and tear are going
to be low.