After seeing the pics of the Dimers (510's) in the Sept/Oct issue of Z-Car mag. with 5-lug wheels, I thought that would be a nice upgrade to one of my cars. Unless there is a car out there that makes a good donor for a 5-lug Z, I think there are better places to spend $ & time.
IMHO it probably isn't worth the effort. I think that something as critical as this really needs to be done correctly & looking at the front spindle of one of my cars, I think you may have trouble maintaining good edge distance to the scallups where the threaded holes for the rotor mtg.
There are a lot of pumped 5.0 mustangs out there w/ 4 x 4-1/2 stud pattern. & this is a heavier car too.
A lot of racing has been done with full race engines and sticky tires on 4 stud z's.
Last but not least, the major fitment problem with the Z is the 0 offset. Most of the current cars have so much offset in the wheels & this is what the aftermarket suppliers are making. Just going to 5 lugs isn't going to fix this problem...
There are a reasonable (OK, maybe 5 or 6) wheels out there in 15 and 16 ~7 wide. These will fit 225-50 tires. For larger sizes, there are sources like Centerline & others that will produce whatever you need....
Boy, for my $.02 that was alot!!!!
tomh