Ply centreboards are unusual in Albacores as they tend to break at the drop of a hat. I have yet to see an Alby with a centreboard box dedicated to the metal foil. I may stand to be corrected on that. Most of the old Fairey boats had boards of a nominal inch and not all were paralell sided due to distortion and build error but this varied between builders young seemed to use a thicker board/ box. Most early glass boats have a slight taper built into the box to make lifting off the mould easier. With this in mind using a pair of inside calipers measure the inside of the c/b box paying particular attention to the front of the capped area as that is where the most distortion tends to be then using the outside calipers measure the thickness of the board. The board should be slightly less than the box.If the board is ply it is more than likely to have swollen, distorted or started to delaminate so check the thickness at various points along the length at the position of maximum chord. If there is significant distortion chuck it away ( I would get rid of a ply board as a matter of course) If ordering new make SURE you have measured thickness accurately. Hope this helps
Sam