Hmm 50kg more with V8 packing aluminium heads? Sounds a bit high.
Have a look at the specs Ford lists for the current Fairlane Ghia.
Difference is 16kg in favour of the I6.
Factors to consider here. I6 used here is VCT version so maybe regular I6 is lighter? V8 used has iron heads. Deduct 20-25kg if aluminium heads are used. Manual comparison may work out more favourably for I6 what with possible difference in weight of flywheel, clutch and transmission.