Problem with 302 heads not many are into porting so the 302 offers very little in performance gain over stock for most.
Plus 273/318 heads was designed for 273 in mind and not as a performance head. 273 head volume and cfm is in similar ratio with 273 displacement as a X is with a 340, a 318 is 47 cid bigger than a 273 and 22 cid smaller than a 340 less so after an overbore. A 1.88 360 heads would be closer to right if you kept volume and cfm ratio for the 318 the same as 273 and 340.
With and overbore a 318 is 12-17 cid less than a 340 and 0.060”-0.030” smaller than the so called magic 4” bore can see these aftermarket heads being that far off. Not needed for 300-325 hp but for the money can’t see a reason not to. But yes a 1.88 360 or a ported 1.88 302 or magnum heads would right inline with 300-350 hp 318.