Hank:
Is these for a Sissel head or did you take someone’s suggestion and make a 12 port out of an integral head 250? Someone started making NEW 3.0L heads for marine use but two welded together would be a little better breather than our siamese port heads. Yes they are made for a 4" bore but, since Douglas is drag racing a 250 with 4" bores well...... ;\)