Bigger is not always better , put 2" or 2 1/2" headers on your stockish dart and it will be a dawg , you might get 8 0r 10 hp more with headers on the 273 , that's might , most of the driving range revs you'll gain nothing .
LOL.... RRR put his arms all around you.... But just so you know, there are 10 second cars out there with manifolds...... Not the easiest way to get into the 10's, but it's been done. So, YOUR 273 with a mild cam will not be shot dead because of no headers....