Quote:
Or a smaller bore A14.

The 1974 A13 as used in the US model B210 was a one-year-only offering & used the same 73mm bore size of the 1200 engine, but the taller block & longer 77mm stroke of the later A14.

Like all A series engines, it's a great design, but the 76mm bore of the 1975 A14 engine makes it just that much better.

If your A13 is in need of a major overhaul or worse, a recondition job, then a later a14 or A15 engine will be a worthwhile substitute.
If it's running fine, then leave it & enjoy motoring at it's economic best.