What wheel stud length is needed?

Front - Cortina hubs

Rear - Sierra

Wheels - RS style 4 spoke Laser wheels

Can't help with your specific question but I needed to lengthen my tina studs and swapped them for granada ones. from the scrappy. Cheaper than buying from rally design etc.
Hope that helps

I used 50mm ones Cortina Hubs Front Sierra Drive flanges on the rear and Alloy wheels fitted, you can actually measure your alloy wheel thickness and then add the thickness of Hub/Flange and then the thread depth you require for your nuts