Are 273 & 318 Heads the same? I am asking about 1968. Thanks.

yes..more or less

68 used the exact same head on both, it was the first open chamber head for either.

It's been too many years but I believe the 273 heads came with adjustable rocker arms because they used solid lifters. The 318's would have hydraulic rocker arms. You can certainly switch the rocker assemblies if needed. I know guys used to seek out the 273 heads specifically because of the rockers. It seems like there were some subtle differences in exhaust port shapes, but nothing too serious.

You're correct on the rocker arms.

68 273s had stamped rockers for use with the new for 68 hydraulic cammed 273. 1967 heads (920 castings)are the same on 273 and 318 but rockers are different (though interchangable if the whole valve train is switched). 66 and older 318 had poly heads and 273s had a head nearly identicle to the 67 head but with a slightly different intake bolt angle(315 casting head and at least one other casting number I can't remember). 68 through 84 318 and 273 heads are virtually all identicle with little more than casting number changes and smog ports on some of the later heads.