I think 80 mph was flying for a 1957 Porsche Speedster and it was heavier steel. They had a max 90 HP! (I think top speed was advertised as 120 mph). A big low mounted front battery would add 40#. A 12.5 gallon extra capacity gas tank adds maybe another 20# over a 10 gallon one. A spare tire and Jack maybe another 40# with tools.
I had a late '65 911 and during a repaint I discovered big cast steel hunks on either side of the front bumpers which I guess were for keeping the front down and providing better balance (F to R). It also had a spare tire mounted low (as a crush zone too) , gas heater, plus jack and tools. It would do an indicated 130 mph but was scary at that speed (fortunately I-81 is pretty straight in VA).