like a few others on here, my original RS had a side tank and the drop tank.  The previous owner installed it as he used it on the highway a bit.  Mine was hooked up so that when the main drop tank was low, you flicked a switch and it would pump the fuel from the side tank into the drop tank.  I never actually used it myself as a pov 18 year old I couldn't afford that much fuel at one time.

The internally mounted aluminium tanks dont have particularly high capacity (10-12 gallons?).
 
Have you considered the possible registration issues within your state of changing the fuel tank?  I would put the coin to something else and stay standard.

lol I cut 25mm off of mine to fit the dry sump pipework

Hey Marti & Matt,
planning ahead is the only way to build or repair these cars.
my biggest concern is earning enough money to keep playing with my toys and these share holder companies like IAG and SUNCORP who own all the insurance company names are destroying the Panelbeating and repair shop industry. People forget who owns the car and who pays the bills. The insurance companies only take the premium and it is the repair shop who give the warranties.
back to it now fellow enthusiasts.
Jim

A few pic from Factory Original Sporting Mk1



I would say it is the right tank turn around.