OP, if you can send those rods back I would do so.
I've learned many lessons the hard way when it comes to engine builds and one of them is knowing what you have and where it came from and not mixing, mish-mashing questionable parts together in a high performance (or really any) engine. Souce as many parts as possible from one supplier (ie all valvetrain components from one supplier) and use ONE machine shop for all your block, rod, crank machining, especially if you are assembling yourself. A competent machine shop will want all the components you are using together at once even if he is'nt assembling the engine.
I honestly don't know why anyone would run reconditioned 40+ year old rods when aftermarket rods that are stronger,lighter and so affordable are available. No offense OP but do some research and talk with a reputable machine shop, I'm sure they'll tell you the same.
If I was doing a stock or slightly hotter than stock rebuild of an existing motor and had all my original rods I would feel better having them rebuilt but buying used rods as you did would leave too many questions for me and I would have a machinist check them out anyway for - cracks, concentricity of both id's, center to center length, proper bolt installation
- all of which is going to cost more $$$$$ but to me would be neccasary for piece of mind and could save you $$$$ and heartache down the line. I'd feel better buying the rods that need to be reconditioned and having them done myself that a set that had already been done.
There are NO
questionable parts in my engine and if you want to sleep at night I would'nt use them IMO.
BTW, love that black 64 post GTO!