MarkC wrote:...is there some sort of locking device on the front brake plate that I cannot see ?
Hi Mark and welcome.
If you're still having trouble with the brakeplate, could be a ridge (or build up of crud) on the inside of the brake drum, have you made sure the fulcrum adjuster (opposite the brake lever on the brakeplate) is fully unscrewed? (As others have suggested...)
Rocking movement isn't an issue with the roller-bearing big-end, I think even new ones rock (!) - as long as there's no vertical movement it should be fine (might well be OK even with a slight bit of vertical play for the use you're intending).
I wouldn't lose too much sleep over the marks/pitting in the bore either, having spent a couple of years running a VH with what looked to be horrible great digs in the bore - not only did it have feendish compression (hot or cold) it didn't use any oil! I've concluded that as long as there isn't a massive continuous plough-line the entire length of the bore it's quite serviceable