Best portable heat is one of these burning the MAPP gas:
Rothenberger Super Fire 2 Gas Torch: Amazon.co.uk: DIY & Tools
Just about the next best thing to oxyacetylene, the garage have taken a seized on prop off a Halmatic 40 with mine and that's 10+kg of bronze to get hot
First use penetrating oil as above then burn 'em
Note of course that lots of heat doesn't do galvanising a lot of good. I don't know if you'd get to the point of creating the sort of nasty fumes that welding on galv will create, but if you do, hold your breath!