Not going to give all the info untill i have done the full conversion and i know it works then i will put some photos up off how i did it, give me a week or so and i should have it done. To wet your appetite i have found that renault 21 diesel savana 1988 ish has the same diameter disc with the same offset even the same size hole in the centre as a magnum disc it just needs redrilling to suit.you can use the magnum caliper with a spacer to widen the caliper centre as the discs are fatter and a little bit off fettling with a grinder it should clear. I am fitting sierra cosworth 4 pots so there is a little more involved with filling and redrilling holes i will let you know.
yes they are im just doing some bits on the axle at the moment so will get on to the front brakes next week somtime, I will take some pics and post them up watch this space!
here are a few pics so far
Renault and standard disc side by side
the centre is a perfect fit on the vauxhall hub
Redrill the 4 mounting holes shorter bolts are needed or a spacer ring made upas the standard bolts are to long
bolted together
A spacer will need to be made to widen the caliper but otherwise it will bolt straight on
I am fitting 4 pot sierra cosworth calipers so i dont need the spacer on the calipers but i do need to modify the hub mountings pics off this will follow
Ahh just had a though the old discs in the pic are ventura ones that are a bit thicker and a couple off mm bigger than than the magnum firenza size .Im not sure about sizes for the 1256 but im sure the hub itself is the same on both cars only the disc size and caliper are different i will find the old firenza /magnum discs out and compare the sizes