>         After reading all the public and private messages and
> changing my mind half a dozen times, I think the best solution is
> that which several suggested right off, namely a 8-kilobyte SRAM
> managed by a 17C43.  The 17C43 has enough I/O lines to directly
> address every line on the 6264 RAM chip plus do all the other
> things I need for it to do.  It will also operate at 16.384 MHZ
> which should give it enough time to handle a 64-kilobit stream as
> long as the ISR is anything reasonable.  It will execute
> 4,196,000 normal instructions per second which should be more
> than fast enough to do what needs to be done.

Well when you're out for a cheaper solution, use a smaller PIC and
74HC logic instead.  One option are ser->par shift registers, another
are counters with parallel output.