Lead fuel additive help

I have just bought a 1977 22286cc SWB. Will it benefit from lead additive in with the fuel or is it possible the head has been converted to accept unleaded fuel, is there an easy way to discover if this has been done already. The engine produces some clouds on start up that has been slightly improved by a new distributor cap, rotor arm and points

Also, any quick fixes for a petrol gauge that works now and again but only with a bad case of parkinsons shake?