Increased Compression and breathing are the biggies. Ted Eaton and John Mummert are great and gracious resources, just ask them. http://www.ford-y-block.com/
Big valve heads, Blue Thunder or Mummert intake, headers and 2 1/4" or larger pipes do a lot. Take advantage of Ted's offer to calculate compression ratio and recommend max milling on unposted G heads. We got the CR too high on my 317 using unposted Gs and had to acquire some 113s. IIRC correctly I'm now running 9.3/1 CR.
The T5 is agreat addition, I used Mummert's adapter on my Vicky hooked to 3.73 rear teeth.
I like the Crane electronic ignition over the Pertronics offering.
The Clay Smith 284 lumpy stick is another worthwhile addition (Mummert calls this his "Cruise Nite Special"). Along with the cam and 1.54 rockers and higher revs, stiffer valve springs will be a big help.
You gotta have the right tools and know how to use 'em.
TC - Austin, Texas