No bummer, heads are very similar 2 bl to 4 bl. They are closed chamber. Same casting #'s for both I believe.
Main difference in Power pak is pistons cam 4bl intake DP distributor and possibly stronger valve springs?
Good to know. Bummer. I was under the impression that the stock 273 heads should be high compression. I may strip the block completely. I will read up on the pistons and performance differences.