Assuming that this is an original untouched engine valve spring tension could be anything from good to poor in which case anything from 5000- 5800 rpm is possible. Early heads like yours have some serious drawbacks. First of all if you intend to put any real mileage on it,
hardened exhaust valve seats should be installed. While you're at it you may as well do a proper three angle valve job and take a .010-.020 truing cut on the block surface of the heads. A bowl port would help a lot as well. The problem with all this is that the cost is such especially after probably having to repair/replace worn guides that you could buy new aluminum heads that flow better for very little more money.
If you want to roll the dice on how long the valve seats will hold up, buy a good set of headers and an RPM intake and top it with a 3310 Holley [750 cfm, vac. sec. ]. Two safe cam choices for a basically stock engine would be the 272 MP purple shaft or a Comp XE268H along with fresh valve springs. You SHOULD always check piston to valve clearance and retainer to guide clearance as well as coil bind with any cam change, but these cams are mild enough that you probably won't have any problems. These cams will work with your stock torque converter although they may pull a little in gear at a stop. If you plan to hammer it a lot a Hemi pan and pickup would be a good idea as well.
If you can afford it the best solution is to yank the original engine and store it and build a good 451 low deck. It will look like a 383, but run much better.
You have a lot of choices, it just comes down to how much speed you want and how many cubic dollars you have to spend.