First thing you need to do is determine which engine you have. It's not uncommon over the years for the original to have gone missing and been replaced with one out of another Alpinr. So there should be a number stamped on the flat over the passenger side fuel pump on the block. If it matches the vin, then you have the original. If it doesn't, then does the dipstick enter the block or the oilpan?? If the block, then you have the later 5 main bearing 1725 engine. Into the oilpan and it's most likely the 3 main 1592 version like the original would have been. Slight chance it could be the 3 main 1494 of the series 1, but only way to tell is by the casing day on the starter side, bore sizes, crank main and rod sizes, etc.
So check what you have and we can go from there.