I recently pulled my head off a slant 6 that's in a 65 Dart.

I had it hot tanked and I painted it and since the valves looked good I slapped it back together. The previous owner had said he had rebuilt it so I didn't think I needed to get it machined. Of course within an oil change or two it started seeping oil. Arg. (yes i torqued it right and in the right order) So I pulled it again and had the machine work done. I noticed though that there seems to be excessive build up on the head around the valves. Is this normal? It hasn't been that many miles since this was hot tanked. Some of it even comes off in large flakes. my random guess is that it's running rich but I have no actual bases for that.

A closer view

and a close up of the top of pistons 4 and 5 notice the pile of flakes in the bottom of 4. yes I will clean them out before assembly, they just fell off the head as I was removing it.

Is that a '75 head?

I think you need to remove the intake valves. Look and see if there is build up on the heads and stems. I am thinking valve guides are leaking oil.

Is there greyish tan crusty flakey stuff on the plugs? Oil.