Max HP that a 4.0L rod can support?

[5-90]

505 has a 600+hp turbo but I don't know what rods.

Eagle forged 6.150" length rods.

Any one know a rough hp figure that the 4.0L can safely handle?

The stock 4.0L rods can easily handle 400+hp and 6000+rpm. Other components in a stock 4.0L engine are likely to fail (e.g. snapped timing chain, cracked crankshaft rod journals) before the stock rods or rod bolts, and the stock composite head gasket will fail if subjected to more than 8psi of boost.
Shotpeening the rods, using ARP rod bolts, nitriding the crank, using a MLS head gasket, and accelerating through the ~5500-5700rpm cam harmonic should take care of the most likely points of failure.

O-ringing the cylinder head gasket (single or double) will also help, probably give more pressure tolerance than using an MLS would.

More machine work, tho.