[Brian]

That rear gallery plug is brass. If the buggar don't shift easily, I usually use the oxy-actylene torch and warm it, it'll come out then. The front plug is steel, and responds to a bit of heat too....
One place that gets overlooked when cleaning [because the block is upside down when cleaning the underside of cylinder block/camshaft area], is; [hard to explain], the top portion [which is upside down] of the main bearings where the webs come down [up?] and where it all flows into the pan rail. Four places, behind the front main bearing, both sides of the centre, front of rear main. Hope this makes sense....
Enjoy the filthy job, but rest assured, cleanliness is next to Godliness.
When scrupulously clean, which means when all machining and cleaning has taken place, and you're about ready to assemble, you can [some people don't like this!] paint the entire inner surfaces of the block [all bits that see oil] with Gyptal. This seals in any impurities you've missed and allows oil to flow back into pan easier. Some say it interferes with heat transfer. Your choice. However, if that paint won't stick anywhere it means that surface is NOT clean.