I've just pulled the front pulley off, to change the cam and noticed a groove .010" deep X .120" wide where the oil seal runs. Is this normal or do I need a new pulley? The new seal I’ve got (GM part) appears fairly rough and doesn't have a tension spring or lip (same as the old one, but I thought it was shagged) has anyone noticed this before? If I need to buy a new pulley, is it a GM supplied part only?

Mine was perfectly smooth if memory serves... Id either buy a used stock pulley from someone on the board (usually 25 - 50), or you could upgrade to an underdrive pulley and gain a little bit.

I've seen this before on traditional SBC's. Napa sells a harmonic balancer repair kit. It's a sleeve that goes over the snout of the balancer.

Definitely pick up an ASP versus repairing/replacing yours.