For starters, make sure you have the calipers on the correct sides (bleeder at the top of the caliper) I've seen it done before and you get a very long/shitty pedal as you can never get all the air out. Thats just one thing to check before you start spending cash, as we all have our blonde moments and do stupid things.
Next go grab yourself some of those plastic brake hose clamps to diagnose the problem. Clamp off all 4 lines. The pedal should feel normal.
so check that first before proceeding
The a31 master will have 2 lines for the front brakes whare as the z32 will have the single line which will be split into 2 at a junction box. You can get around this by installing a junction box but will require altering your brake lines. Then you can take both fronts off theck the then both rears ect you get the picture
Then if it is the master and you really cant find one to suit go get your master bored out if you end up having no luck, but abit of a pricey option. But surely there is another master out there to suit.
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go with this one