56cm x 54cm. Gazelle Champion Mondial AB frame - Piet De Wit model, 531c. Wrap over seat stays, Campag ends, engravings on brake bridge, bb shell and on the aero fork crown.
Paint is alright but it really would benefit from being refinished.
Why would it benefit from being refinised? Judging from the pics you provided: If you give it a quick clean with WD40, clean the little scratches away with a mild polishing compound and wax the frame afterwwards, you save a lot of money and preserve the original paint, with probably a quite good result.
Btw Piet de Wit were a successfull Stayer champ. Nowadays he carries a bike shop in Wormer, NL. Probably your frame was originally sold in 'Zaanstad' area, a little above A'dam. The area were Wormer is part of.