Avoid butchering the S/A mudguard. The deeper valance will cause problems with adaption to fit and aesthetic result, plus the blade is of more value to someone else.
Musky is on the money here, but any B or M plunger blade, original or repro will be an easier knife and fork fit. They may have differing brackets and minor differences, but the pressings are substantially the same across the A,B,M Ranges. Lack of a hinged rear section as on some repo's is easily overcome by a convenient brick under one leg of the main stand. This raises the bike enough to get the wheel out, and is far quicker even if you have the hinged section. Preserves that concours paintwork.......
Swarfy.