I have seen it done to an xe 351.
Theres a guy in perth whos in the rydin dirty car club who has twin mixers on an xe falcon on straight gas.
Seems to go pretty good and looks fairly neat under bonnet,from memory it ran a mid 13.
Numberplate is hypo xe i think, sorry about the vague info but thats all i got .
So yes it can be done.

For a 5.8 you should only need a single tank : Perhaps a better service line though (not copper in most cases). They work well, but need a little tuning.

There are also options like the GRA Dual throttle body setups .

Cheers

Nigel

a mate of mine has done it in a XA ute, was a few years ago and the car has been sold.
he built a 351 C to run only gas, 11:1 comp, mild 4v heads, biggish hydraulic cam and cut down tunnel ram with 2 425s
had 2 gas tanks, one under the floor and one in the tub, it ran nice got great millage but made crap power way less than he expected, and way less than it would have with a single 4 barrel
He mucked around with it for ages, I think in the end they found the tunnel ram, even cut down was to big for the engine and the 425's where to restrictive
With a bit more planing it would have worked well, Ill call him see if I can dig up some pics