Handlebar stem: (This may have been covered earlier - in which case please ignore.) This age of kit typically has an wedge-shaped (or truncated cone if you want to be pedantic) expansion nut at the bottom of the long bolt that passes through the stem. Tightening the bolt lifts the wedge upwards and causes the end of the stem (which has 1 or more slots cut in it) to flare out, hoding it into the head tube. When you loosen the bolt, the wedges stays where it is and the bolt rises up out of the stem. You need to knock the wedge downwards (hammer+ block of wood or mallet) to push the wedge out of the stem. You can, but don't need to, knock the wedge nut out entirely and it will drop through the fork. You can then invert the frame and run penetrating oil in every day for a few days to try and get it between the stem and the fork tube. Supporting the forks (big bench vice?) you may then be able to persuade the stem to start moving side to side and eventually out. Bit of heat on the stem may help but if all else fails you may end up having to cut/dissolve it out - which is tricky to do without damaging the fork tube. If the stem comes out without damage it can be reused, but make sure you put some grease on it to save the next person from the same grief.
Frame identity: The chances of you identifying the make from the frame number are almost zero. Better off just sanding the rust down a bit until you discover a colour you like and using that. It's not like the classic car market for this kind of bike. There's a little chip on one of your pics that could be bronze?? Best make sure that none of the rust goes all the way through before you think too much about colour. You may yet have to put it back in the sea.
Brake blocks: Check out Fibrax (who I think have an ebay shop) and I'm sure they still do something suitable.
