Looks good except I would go with C heads over the Bs. Yeah the B heads can make good power but the C head will do better throughout. If you are dead set on staying with the B heads I wouldn't port them, they don't need it. Valve job, IMRC delete and run them as is. You can also make 650whp with stage 2 ported PI heads if you were ever thinking of staying 2V. TFS head obviously will too.
A 76mm should get you to your power goal and stock 96-98 Cobra cams will get you to 650 no problem.
Before you start have you ever thought of a Coyote swap over a modular 4V build? Price them both out and I'm willing to bet it would be cheaper to do the Coyote.
2000 Mustang GT Steeda #0048 34k miles. 99 Cobra 4V swapped, FTBR IRS swapped, exhaust, tuned by James Gordon.
Just because I give you advice, doesn't mean I know more than you. Its just means I've done more stupid ****.