The D-dart used the same intake as the other 4bbls.

308 heads are a terrible option as compression will be really bad like mabey 6.5 to one. The valves will need notching and it will have a ton of crevice volume and no quench at all. The big ports will keep the velocity too low for any low speed performance.

The best head for a 273 is the 920 heads from 67 273 and 318s only, you can use what ever normal SB intake you want and they have the smallest chambers, valves that fit without notches, more flow than the 302 head with out being too much like the 360 heads.