Okay, I'm trying to press out the barrel pin of Romy kit - I very carefully put it on my plate, then apply pressure - but it looking like I'm continually bending the gas block.  What's the best method of using a press to get out a stubborn barrel pin?

I've soaked it in anti-seize,  the problem is that it's rolling onto the rear sight block when I apply pressure - I can't even really PUT a lot of pressure on, as the trunnion wobbles and then rolls onto the rear sight block

You need this

Curtis will take care of you.

Use a small piece of 2x4 under the trunion. Drill a hole in the wood for the pin to go through, flip your sight up and out of the way or take it out. The spring under the rear sight has to be depressed then the sight assembly can be removed.
Soak the pin with Kroil, it works better than any other penetrant. Candyman mentioned applying heat on one side of the sight block/pin and putting the Kroil on the other side. The heat will suck up the oil in the barrel pin hole making it much easier to punch out. I haven't tried it but I believe what socandyman says!
We've had 5 hard ass barrel pins  to drill out on various kits. Three Roms and two AMDs between 8 or 9 guys with 17 oir 18 kits. You get a real beast every so often, almost impossible to punch out with a press even!