what heads to run on a 273

302 casting heads are found on late 80s 318s. They feature a swirl port design and just the right size valves for your engine. I'd also recommend an Edelbrock preformer intake (not the rpm version) for your car. If you do a quick search using the search feature on the site, you'll find tons of info on the 302 heads.
Also the 273 and to an extent the 318 are more costly to build, it's cheaper to throw a 360 or stroke it to a 408 less and make more power doing it.
Not that I'm trying to sway you against the 273 but other will throw that info out there.