[Jac Mac]

I have seen figures for the Flip Top of either 1600# or 1800#, since that was essentially a 289 leaf spring chassis with an ultra lite alloy shell & alloy 390with very little in the way of creature comforts etc its probably as light as they have been--- should never say never though! On that basis you should with all the light bits available today build a SB copy that is down around or below that figure.
Alloy block-Heads-Ultra lite crank rods etc-Mag Case T10- Mag Case 9" IRS-. If you have the $$ I am sure it can be done!
Im sure the sanctioning bodies that decide what roll cage you have to run will be a fly in the ointment though- plus extinguishers-helmets-nomex-fuel cells etc etc, -----all that stuff that was not deemed necessary back in the 'good ol days'.