Dear ray
i used this rtc in one of my project
but on that project
p1 was common for lcd data and rtc data/addr
p0 was reserved for keypad
At first i am sure you must discrete lcd control pins
from rtc control pins
it is not necessary using 74LS08 for isolating lcd.
If you don't read from lcd then db0-db7 are isolated from rtc.
because lcd and rtc routines don't execute in the same time
so it is enough to disable lcd when it doesn't need
and disable rtc when...
in addition when you want to reading a port
you must first write 0ffh on the port
Mov P1,#0FFh because of 8051 internal latch situation
(see datasheet)
so before movx a,@rx you must first send 0ffh to p0

you apply this matter in your following code!
MOV DATA0,#0FFH
MOV A,DATA0
JB ACC.7,not_ready

is the following code ok?

next1: CJNE A, #0BH, next2
MOV A, #42H
JMP write1
next2: CJNE A, #0CH, next3
MOV A, #42H ;i think 43H is right
JMP write1



...
...
...
at last

I Hope this will be useful for you!
Mehdi