The caliper looks like the basic Girling Type 14 model which is OEM fitment but it's hard to tell without a scale or detailed photo. If the slot between the two halves is too small to fit your disc you might have a modified brake system. The type 14 fits the thinnest disc from the period, typically 9.5-10mm thick depending on source whereas the visually similar type 16 caliper has a wider slot for 13mm discs. The Type 16 is much bigger and heavier though, but hard to tell without a ruler/scale on the photo.
The details of OEM stuff are;
Discs:
Elan, Europa, Spitfire, Herald
Diameter 232mm, Thickness 10mm, Height (from hub) 27mm
Elan +2, GT6 Vitesse (2L)
Diameter 245mm, Thickness 13mm, Height (from hub) 28mm
Brake Calipers:
Type 12 & 14 as fitted to Herald, Spitfire, Elan, Europa
48mm diameter pistons
3.25" (82mm) bolt centers on mounting lugs
Type 16 as fitted to GT6 & 2L Vitesse models
54mm diameter pistons
3.5" (88mm) bolt centers on mounting lugs
To confuse matters even further, there were larger calipers as fitted to some Ford cars which have Type 16 pistons but 82mm mounting centers and the 232mm discs.
Also there's a Triumph TR7 front caliper which looks similar but has a larger piston but no details.
I'd measure up the caliper and see where it fits in relation to the above. Then look at the width of the discs you have fitted on the car and we might be able to work something out.
Brian