273 vs 318

Like rmchrgr said on the heads. Otherwise, you would mostly be wasting time with the head swap. The 302's need work as would the stock heads to achieve this time bracket. (12's) Though a good prep and valve job for 13's would be adviseable.
A Edelbrock Performer intake is what you'll need.
I'm not so sure I'd do tti's since the header tube is large.
A Comp Cam designed for exhaust manifolds is what I'd run.
I'd also replace the time bomb rear with a 8-1/4 min.
The 727 is slower but stronger. And not really needed.