Have just joined so apologies for a late reply. I have three Grubb 'Perfections' or at least I think I have. Its difficult to identify the different lugs. One sold to me as an Exquisite is on the Classiclightweights site and has quite different lugs to yours. I have another Grubb which I take to be a Perfection which has lugs like yours but without windows so it may be a Cote D'Azur. the other is a Holdsworth Perfection. Either way your frame is a top of the range Grubb and is well worth sorting out; both of mine ride beautifully. I should think that 49/50 is about right for age.
Hi there and welcome.
I have found a new owner for the frame as it's way too big for me. I'll be posting it to him shortly and hopefully he'll be able to get it all straight and up and running.