Well looking at the rego papers for both the EB & EF & there is only 5kg differece between the i6 EF & the V8 EB!

wow! EF i6 sure are fat C***

5.0 Windsors only weigh about 15kg more than an SOHC I6, fit alloy heads to the Windsor block and it becomes even lighter.

I thought the difference was more like 30kg, but the fitment of alloy heads would still fix that.
As far as the EF weighing more than the EB, safety, comfort & noise reduction all add weight.
EB will have thinner door glass, less anti intrusion & body stiffening metal (eg. the roof pillars got progressively stronger throughout e-series development, they could hold 3 tonne by EB2), no abs (optional from may 92), no airbags, no belt pre-tentioners, no smartlock (until mid october 92), less noise damping etc.
Then there is other posibilities like the T5 weighing less than the 4speed BTR (XR8 or retro-fit only), base models having no power mirrors, power windows, no LSD etc.

Hope this sheds some light for you.