I was wondering how to identify the sort of engine I have from markings on the block . So far I know its a 4.1 x-flow but dont know if its leaded or u/l , comp ratio , type of oil it should have (noisy tappets , suspected oils abit light ) , any help woulbe much appreciated .

On the side of the block near where the coil mounts, are some numbers.
Unleaded engines have the prefix 86 DA ( XF ), leaded ones have 84 DA ( XF ) and earlier. So 83 DA are XE blocks. Both the XF blocks have a one piece oil seal and early blocks have a rope oil seal.