I'm not old enough to know from personal hands on but I strongly suspect that the fork blades are common, for that era, 531 blades. Likely a 28x16 oval and around 1.1-1.3mm wall at the top. Besides the top oval shape, what is also likely different from current blades is that the tips were often of small diameter for a longer portion of the blade's skinny end. All the easier to bend this or that way
I might have a pair of 531 blades still but old 531 sets come up on EBay every so often. Do you have the crown and steerer already? Andy