My March built LA 70 Road Runner has a tubes tyle jack as well. However the base, tube and jack mechanism do not look like yours. Was your car built at the end of the model year? Maybe there was a change of suppliers or something? Very interesting as I have never seen a base, tube or jack like yours in any 70 B body (LA, St. Louis or Lynch Rd.).

70 Road Runner 383-4 4 speed FJ5 & black guts
70 Charger R/T 440-4 4 speed FJ5 & white guts