OK, felling like a bit of a dummy..... although I have to say the Pelican website could use a bit of a tune-up. They list the standard guide as .514" and the first oversize (which I bought) as 13.08mm.
Stupid me for not doing the math. I laid awake half the night wondering how I was going take a .0005 cut with a lathe that I'm pretty sure has a mind of it's own at least 2 or 3 times that dimension
Thanks, Craig, for the wake-up call!
PS - any advice for cleanup of the guide bores in the head and recommendation for a common lube for install? WD40? Or should I order some mutton tallow? will bacon grease do? gaucamole?