16 X 3 will fit as long as it has 1" bearings , although I think a 08 rear wheel is 16x4 . Sportsters up to 03 had 16x3 ,

Front wheels will also go on the rear but the Bolt holes are diffrent , Front are taped 3/8 for the Disc and Rears are taped 1/2 on one side for the pulley , so you can re-tap them to 1/2 , as far as I know the offsets are the same

are you sure about the bearings being metric , Ok my bike is a 06 Sportster but  it has 1" rear and 3/4" front  axles, I couldn't see HD moving away to 25mm on both . Big Twins have 1" front and back

Same with the tyre size up to 03 Sportsters have 130 and after that 150 tyre thats why I think it should be 16 x 4

ok

I Apologize , I just got out my Bible ,, the JP Cycles Catalogue and yes all 08 models have 25 mm Axles ,,,, ,,,,
well , to quote Gordon Ramsey " I be F##ked "