Welcome to the Team Don!
You are still within the power range of the ten bolt rear end. You are bumping up against the upper limit at 350 horsepower; but with street tires, you should still be safe. A PosiTrac rear end from Eaton will not only make your driving experience more enjoyable but a little safer and help the rear end to last longer.
As one tire spins, the gears inside turn at twice the tire speed. They are riding on a bronze bushing without the benefit of force fed lubrication. So the side and spider gears will weld themselves to the differential case if you do it often enough, or long enough, resulting in the rear end breaking.
The weakest part of the 1966 ten bolt rear end was the axels so an upgrade to aftermarket axels and all new bearings and seals would be a good thing. For the amount of money you will pay for a new Eaton PosiTrac differential, a new gear set, new bearings and seals and shims to set up the rear end (not normally found in a rebuild kit) plus the price of new axels you are close to the price of a store bought 12 bolt rear end from the aftermarket (Moser, or Currie for example). I would compare the total costs of a new 12 bolt (that can handle nearly twice the power of a ten bolt with the right parts in it) compared to rebuilding your old ten bolt.
Don't forget to include labor as it is not a bolt in experience to set up a rear end with new gears (it can be done but if you get the set-up wrong you can destroy a set of gears in ten minutes driving time). If you stay with your original gear set you just reuse the shim packs you have now and replacing the bearings isn't that difficult (though it will require a hydraulic press for the pinion bearing and a strong arm to crush the new crush sleeve).