Another thought...
You might be better off selling that 289 to someone that needs it for a restoration project... not sure if it'd get a premium price or not though. Assuming it would, I'd recommend picking up a 302 from a late 80's early 90's mustang GT. They came with forged internals and can be pushed pretty far... check out this article :
http://carcraft.com/techarticles/50452/
If you do go that route, be aware that one year (i think 87) had flat top pistons that won't work with some aftermarket heads too... I'm not 100% sure on that though, so just double check if you do it!