One needs to look mainly at the bust style to differentiate between the 5d sub-classes, and also at the crown end ornaments to help distinguish between 5d2 and 5d3.

5d1: - Crude bust, with half fleur crown ends

5d2: - More realistic bust, as per later coins e.g as for 5g, but with half fleur crown ends

5d3: - Neater bust, finer than other voided long cross pennies. Distinctive sharp crown ends rather than half fleurs. Distinctive central fleur.  Often has a split crownband.