All 260, 289 and 302W(non BOSS) heads have the same size valves (1.78"I x 1.46"E) and ports, even the rare HIPO 289 heads have similar small valves. The only variation in the small block head was combustion chamber size and shape, and smog bumps in the exhaust side. The exception to the rule is the 1969-1974 351W heads, which have larger valves, (1.84"I x 1.54"E) slightly larger ports and much larger combustion chambers. The obvious disadvantage of the bigger combustion chambers is lower compression when used on a 302, but the benefit of those larger chambers is unshrouded valves, meaning better flow, especially if you increase the valve sizes. You can mill the '69-'74 351W heads to some degree, and also have the machinist install thicker valve seats, so that the closed valves protrude slightly into the chambers, both tactics will decrease the volume of the chambers for more compression. You can also use pop-up pistons to get the compression way up, but then you will impede the flame front travel across the piston, and will lose some efficiency compared to a similar-compression flat-top piston setup. Years ago, it was a good economical tactic to use the milled 351W heads on a 302 with just the bumps in the exhaust ports removed, but with the cheap availability of serious flowing aftermarket heads for the 302, the 351W route probably isnt the best choice in most cases. Especially since those old 351W heads arent all that common anymore.
