You should be fine for now w/ the 67mm TB. I would recommend the 70, but I don't know about a 75mm. W/o boost, I don't think I'd step up to more than 70. Drive it w/ the 67 for a while, and when the time comes try a larger TB. In fact, have it dyno'd before and after and you'll know 100% how it affects your hp. You may want a larger MAF if you go to a 75mm TB, though.

 

Well the guy that runs a mustang and lightning shop right down the street from me has told me he has never used anything bigger than a 65mm on a stock block because it will support all the hp that block can handle. In the shop that day he also have super charged 5.0 with stock block and was putting down over 550hp w/ 65mm tb. It did have the trick flow r intake and tw heads and a custom cam.

 

i wouldnt go any bigger than 70mm or youll over feed your engine you should lay down 350+ im getting ready to get some e7 heads worked over and a cam and i was told that i should lay down 280-300 hp and run high 12's without juice

 

Mrbigshot is a little too leany on the horsepower numbers. You have almost the exact same set-up as me now. Before I ran a Z303 cam with alot less duration, A GT40 intake which is a street intake and it made 325 RWHP and 330 RWTQ.

Now I switched to the exact same cam as your running plus and Trickflow R Intake. I think it should be close to 350 RWHP at about 7000 RPMs.

The 67mm will cost you about 5-7 RWHP up top but thats barley noticable.