Im also about to do this on my rally car, Im planning to weld an aluminum frame up *in* the car around the mounting points, curved round bar and pipe to get most of the coutures. PVC piping for gauge pod forming. Nav computer and fire extinguisher will have plate backing to give a strong mounting fascia. Temporary plates for a switch panel fascia. Once the frame is done ill remove it from the car to do the rest. Elastain cotton fleece will be stretched over the frame. Then judiciously manipulating the stretched fleece to what I want. Washers can be stretched to mount points, hog clipping to the framework in some places to give a negative curve, plate protrusions to give fascias, open rings to allow for roll cage legs. CA glue can be used for material to metal bonding. After the material is right, glass it out. Remove any unneeded framework after. PVA for anti stick if needed.
Thats a link to a thread in another forum of a guy who did the same. Browse through and get some ideas. Basically he cut up the old dash and use the plastic backing for mounting and worked off that, wooden framework and pvc piping for the rest. There are some other dash projects on that site, you will get allot of info there.
It will require a bit of fg knowledge, hope it helps.