Regarding tyres, my one piece of advice would be buy a decent set and don't be tempted to save a few pounds on budget tyres thinking "it's a second car..." second or third car, you still need grip. and the tyre is the only thing that keeps you planted. But i would tend to take a different ...

The problem is not removing the relief valve, it's getting it back. access is limited and the spring is strong. ideally 2 people, one above and one below. john twist has a vid of a technique but to be honest it's more common sense than anything really. i also have only removed it with engine out. so...

well i hope it works for you. attached is a pic of mine when i removed it some years ago. the pile of crud is just a fraction of what actually came out.
G(raham)
[attachment=0]crank breather.jpg[/attachment]

Dave When you say open pipe to cloth filter- are you referring to one of those mini K&N type ones that sits on the top of the pipe. If so, i suspect your problem is as follows. i am guessing your front tappet cover gauze has been removed. not uncommon as after a few decades without cleaning, the...

Peter
Interested to hear how you went to 10.5:1. what is your head chamber volume on the 12H2709? tight squish i assume and/or shallow dish pistons? ie shallower than stock?
G