Quite interesting im looking at doing something similar with HR31 Rear backing plates and drums rather than the R32 ones.
Hopeing to use 2pots skyline calipers.

Now im still working out weather to use the datsun rear arms or convert to coil over springs and use the HR31 Arms which will pretty much be a bolt up job.

What 5 stud hubs are thoes you are using???
I have 1 Cedric 5 stud hub to work with and so far its exactly the same as a R31 hub except it has the extra wheel stud.
Id love to atleast see a pic of some Z31 stubs or get another cedric stub but its so hard to find.

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Past:
A10 160J Coupe
R30 Turbo Manual
Present:
KP710 160JSSS Coupe (My Standard Car)
KP710 160JSSS Coupe (My SR20DET 6Spd Car)
KP710 140J Delux (New Road Car)
KP710 Parts POS

anyone know the caliper bolt spaceing between z31 calipers 3" or 3.5" cheers

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-1969 1600 SR20

more info here: http://wiki.r31skylineclub.com/index.ph ... rake.2FHub