Since I see the occasional thread about installing a 6 speed in the A70 chassis, I found the following information that I had stored away. The bolded ratios are the ones that already come in an A70 chassis, however, it shoud be possible to use 8" differentials from other models, some of which may have the taller ratios which will allow first gear to be actually useful.
To do so, I believe that you'll need the 8" ring gear in a 4 pinion configuration. I don't know if the LSD clutch pack can be installed into a differential that didn't already have it, but you may be able to find one that already has it.
Some combinations of ratio and ring gear may exist, however, this information will decode the data tag information.
Axle Codes:
First Digit = Ring Gear Diameter
A=138mm
B=145mm
C=6.25"
D=6.62"
E=7.1"
F=7.5" ('82-'86 A6 chassis)
G=8" ('86.5-'92 A7 chassis)
H=9"
J=9.25"
K=9.5"
L=10.5"
M=12.5"
N=13.5"
P=14"
R=162mm
S=6.38"
T=6.7"
U=6"
V=10.6"
W=15.5"
X=142mm
Y=158mm
Second and third digits = Gear Ratio
01=3.30
02=3.36
03=3.545
04=3.556
05=3.70
06=3.889
07=3.90
08=4.111
09=4.222
10=4.375
11=4.444
12=4.625
13=4.79
14=4.875
15=5.125
16=5.286
17=5.60
18=5.714
19=5.833
20=6.167
21=6.667
22=6.78
23=6.833
24=7.64
25=4.556
26=5.571
27=3.364
28=4.300 (MA70 NA)
29=4.100 (JZA70)
30=3.727 (Late '89+ MA70 Turbo)
31=3.909 ('87-'89 MA70 Turbo)
32=6.591 OR 5.583
33=7.503 OR 5.583
34=6.781 OR 4.786
35=7.636 OR 5.600
36=4.778
37=3.583
38=3.417
Fourth Digit (number of pinion gears / LSD or Open)
2=2 Pinions Open
3=2 Pinions LSD
4=4 Pinions Open
5=4 Pinions LSD
To do so, I believe that you'll need the 8" ring gear in a 4 pinion configuration. I don't know if the LSD clutch pack can be installed into a differential that didn't already have it, but you may be able to find one that already has it.
Some combinations of ratio and ring gear may exist, however, this information will decode the data tag information.
Axle Codes:
First Digit = Ring Gear Diameter
A=138mm
B=145mm
C=6.25"
D=6.62"
E=7.1"
F=7.5" ('82-'86 A6 chassis)
G=8" ('86.5-'92 A7 chassis)
H=9"
J=9.25"
K=9.5"
L=10.5"
M=12.5"
N=13.5"
P=14"
R=162mm
S=6.38"
T=6.7"
U=6"
V=10.6"
W=15.5"
X=142mm
Y=158mm
Second and third digits = Gear Ratio
01=3.30
02=3.36
03=3.545
04=3.556
05=3.70
06=3.889
07=3.90
08=4.111
09=4.222
10=4.375
11=4.444
12=4.625
13=4.79
14=4.875
15=5.125
16=5.286
17=5.60
18=5.714
19=5.833
20=6.167
21=6.667
22=6.78
23=6.833
24=7.64
25=4.556
26=5.571
27=3.364
28=4.300 (MA70 NA)
29=4.100 (JZA70)
30=3.727 (Late '89+ MA70 Turbo)
31=3.909 ('87-'89 MA70 Turbo)
32=6.591 OR 5.583
33=7.503 OR 5.583
34=6.781 OR 4.786
35=7.636 OR 5.600
36=4.778
37=3.583
38=3.417
Fourth Digit (number of pinion gears / LSD or Open)
2=2 Pinions Open
3=2 Pinions LSD
4=4 Pinions Open
5=4 Pinions LSD