Issue No.07 - July (1970 vol.19)
T. Kameda , Dept. of Elec. Engrg. University of Waterloo
Two of the three authors who did the first extensive work on 2-way pushdown automata  consider multitape and multihead extensions of 1-way and 2-way deterministic and nondeterministic pushdown automata (PDA).
T. Kameda, "R70-23 Multi-Tape and Multi-Head Pushdown Automata", IEEE Transactions on Computers, vol.19, no. 7, pp. 659-660, July 1970, doi:10.1109/T-C.1970.223010