Without a set of rules in front of me ,it is difficult to say what to do. What is allowed to be done. And more to the point what have they told you can't be done !! Tony's car never ran as a sports sedan but I guess you are just using it to define the style of modifications. A lot of weight can be saved by using lighter components in the suspension which in turn results in better and sharper handling. These mods can be done step by step as finances allow. I'd start at the front with the struts. Can you shorten them? 50mm out of the pushrod and body is a start. This compensates for the threaded sleeve you add for the adjustable spring seat and all of that can be made of alloy . Alloy calipers shave weight as do hubs. Drilled vented discs on alloy hats .Fiat 124s and 125s have beaut alloy racks that work a treat in 1200s. Are you allowed replica bumpers and alloy mounts of course. If you are required to use leaf springs remove all the leaves and use coilover shocks. Alloy drums from 240Zs work well and are lighter than a disc set up. Do you need to run an alternator , can you run a total loss set up and just recharge the battery. The steel panels are pretty light to begin with but you could still remove all the inside bracing on the boot and bonnet. I always follow the practice of looking at the weight which must be added eg rollcage balanced by the equivilent weight that can be removed. Aircraft parts suppliers have some amazing fittings and fastening to save weight in planes which can be used but they can be expensive. Alloy driveshafts fall into this catagory. And another hint that a lot of guys miss, keep the exhaust system simple, tube is weight and mufflers are worse run the bare minimum and as short as possible out behind the drivers door to the side if the rules allow it. If you have already tried all of these tips its time to acid dip the shell and engine block !!!!!!