For me 'period correct' has more to do with you what you can readily see. All though, I really appreciate a truly well done and authentic down to the last bolt replica!
But the BIG concerns, for me, are:
Body shape, wheels, dash layout\gauges, gear shifter, seats, interior in general, steering wheel and engine. The car needs to 'look right' first and foremost. As for the myriad of other details it comes down to personal feelings. There are some things I just cannot accept on MY replica but I'd be fine with it on YOUR replica. I LIKE running a flat tappet cam, not that anyone can SEE it, but I know it's in there and thats important to me!
I certainly prefer a round tube 'correct' frame, but I wouldn't sacrafice the correct look of the body just to get one. And SOME have! Solution? Kirkham or CSX come to mind...
In the end it is good to strive for as much original detail as possible and be happy with as close as you can get within your budget.