Just de-burr the drain holes. The allen head plugs go into the oil gallery.

 

yeah you cant have too big of a drain hole, the faster the oil gets back to the pan the better. no worries there but if you just dont like the look of the as-cast holes deburring them is fine.

aftermarket heads are always a plus, but your heads can be worked to make some pretty damn good power especially with the forced induction you are talking about. If your going to buy aftermarket, I recommend getting them bare so you can choose your own valves and get springs matched to your cam. roller rocker setups are available for these motors as well and are certainly worth the money IMO.

word of wisdom coming from a cylinder head machinist - use Ferrea valves designed for turbo applications, getting stainless valves (like the ones that come in assembled aftermarket heads) doesnt mean they will handle the extra heat they need to when using a turbo.

http://www.ferrea.com/catalog/2006Domestic.pdf

they carry FE valves in their "6000 Series" but you would have to ask them if the exhausts would be ok for turbo. if they arent then they can custom make FE exhaust valves that would suffice in a turbo setup from their "Super Alloy Series"

all that being said, i'd still turn that thing into a 428. hell, with quality parts, a excellent balance job and lightweight valvetrain you could spin the hell outta that big block which would be awsome with forced induction.

 

Well that post was full of information. Thank you.