I was going to use the 1985 318 swirl port heads on my 273 too, they are easy to find in the junk yard and have the same valve size as the 273. The casting number ends in 302. Its a closed chamber head and then you can use flat top pistons to get a good quench, its also very efficient (compared to 273 heads) and you can use any modern 318 manifold. I was planning on using an older LD4 manifold from Edelbrock I see them on Ebay every so often.