The accepted safe power level of the Boss internals is about 800 to the wheels from lots of ppl who have/had them. If you can get yours replaced with a Boss shortblock DO IT! Also have them put in some Boss exhaust cams while they are at it if you can. The intake cams are the same.
Just be aware that the Boss internals are not truly "forged" but they are a lot stronger than the GT stuff. Lots of pplz in Modular-Land use the Boss rods because they are $160 for a set and are a direct drop in for the 4.6L and are strong as hell.
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 ****.