Noel,
Not to get too anal, but all the Sunn heads I've had (over a dozen) used oval-head machine screws rather than pan-head. The pan-head has more of a square shoulder and the oval-head has a smooth curve (looks like a round-head screw that has been squashed). Pan-heads are flat on the bottom side of the head, whereas oval-heads have a tapered surface that fit nicely into the finish washer. Sunn's finish washers (similar to those used on Fender amps from the late 60's - on) are held in place by a tiny rubber o-ring. Then there is the question of nickel plating or chrome plating! I know, way too much info. When you restore pricey Fenders or Marshalls, getting these little details right is important. That being said, pan-heads will work just fine....securing the chassis inside inside the cab so it doesn't bang around is the most important thing! Glad you got your baby fixed.
Ryan