I think the 1500cc had a 3 bearing crank, whereas the 1725cc was upgraded to a 5 bearing crank (although early 1725cc also had 3 bearing cranks but didn't last too well).
It's easy to tell them apart, simply get a pair of x-ray specs from a 1978 copy of Whizzer & Chips
The 1494cc engine has serial numbers prefixed "C" (CKD -"CB")
The 1592cc engine has serial numbers prefixed "2C" (CKD "2CB")
If you've got a diesel the serial numbers commence at 7000251, but then if you've been putting petrol into a diesel I guess that's b*ggered it anyway[}][}]