An ebay find...
View attachment 410265
...an Enco boring/ facing head with a 1 inch straight arbor and an R8 arbor. It was listed 'for parts' because the seller didn't have any way to test it for function.
I took a chance on it... and it seems to be in good condition. Everything works very smoothly, and it advances 0.005" per revolution. I don't know if the advance is adjustable or not... I doubt it.
I've used the Criterion boring/ facing heads a good bit at work, they are not adjustable for the advance... I've also used a big one, I think it was a Wolhaupter, maybe 9" diameter... it was adjustable.
-Bear