Rear wheel spacer advice

[fozworth]

I've just fitted my BBT sprint stars to the bus .Rears are 5.5 with an offset of ET25 .I was told by someone on here that I would need a 5mm wheel spacer to allow the wheel to stick out enough so the centre cap cleared the castle nut. But looking at the wheel I'd say it needs a 10mm spacer to clear so with that in mind I guess I need long wheel bolts .wheres best to get them or am I missing something with the spacer size?

 

[radish]

EBay or midland wheels