DEC Unibus Interface ICs

The DEC PDP-11 Unibus Handbook identifies three standard ICs for use when connecting to Unibus lines: Bus Receiver - 8640 Quad NOR Bus Transceiver - 8641 Quad Bus Driver - 8861 Quad NAND It seems to be generally agreed that the 8861 driver/transmitter can be substituted by the 7439 Quad 2 Input NAND Buffer O.C. There seems to be no recognized physical substitute for the 8640, at least in part because it uses the 1 & 8 pins rather than 7 & 14 pins for GND/VCC, respectively (see Figure 1-25). Is that correct? What have folks been doing when needing to physically replace one of these -- substitute from a sacrificial module? For new designs, or rewiring old ones (dead-bug?), is there a generally agreed logical substitute for the 8640? Unibus Handbook Figure 1-30 does specify the RC-equivalent input for this IC but I have not as yet tried to cross-walk it against well-known SN74xx-series chips. I imagine that I'm the umpteenth person to encounter this problem, so before I try to rediscover fire I'm hoping that someone else could share their torch of knowledge :->? ----- paul