what heads to run on a 273

Personal experience-
'85 302 2-bbl vs '65 273 2-bbl heads, on a 273:
273 heads have larger ports by a substantial margin
302 heads have slightly smaller chambers by about 2cc
273's made better high end power, sluggish below 2k rpm
302's made better low end torque and more responsive, less top end rush

302's need a lot of porting to get the potential people talk about.