I can't understand you very well.
This ADC can't write to ram for this you need a DMA device. The '52 must read the ADC and put the data in RAM.
Do you want a continus flux in both.

You can control both devices with interrupts.

Why an external ADC an not an internal?

Why 64K of RAM?

There are some derivates with 8K on chip RAM and Analog inputs. This could be a sigle chip option.

You can do somethink like this:

Serial interrupt:
pull from FIFO
put the data in serial port.


A/D interrupt:
get the data
push the data in to fifo.


The main program must inicialize all vectors etc.
The push an pull routines must control overload of fifo stack..

Regards.