Neil,
Not sure what size spacer you need.
Is the nut hitting the rim ?
I guess it all depends on the offset of the rim. I would just mock it up and make a wooden spacer or something before ordering anything.
BTW, also check your steering clearance, that was a big problem for me.
As to the studs, yes, if you are going to redril the drums, and use a spacer you will need longer studs.
Are you going to use press-in studs ?
Depending on what nuts you are going to use, measure carefully.
I first had studs that were too short, then I had studs that were too long (couldn't tighten the nut all the way).
My whole wheel experience has been a big PITA. First I had blank drums/rotors drilled by a local machine shop, but the bolts did not align properly with the rim, so I ordered custom rotors and drums.
Then my front wheels hit the beam under full lock, so I had to get spacers. Then I had to find the correct studs and nuts.....
All I can say is, do your research it will save you money and aggrevation in the end...
Sorry for the rant.....
Rob.