Graeme, the s/c pulley is prone to slip if it doesn't have a really good tight belt contact as far around as possible. I think both of these may be slightly less than the stock 2 belt setup. The w/p doesn't need much as it is pretty low resistance.
I have to make a small 2 or 3 prong fitting for the new idler. That's the only work I'd save and maybe only temporarily at that. I think I'll redo the coil packs in the stock location. That means I can extend the bolts a bit and have the mount run there.
With the crossover and the manifold wrapped I don't think heat will be an issue with the coils. The small space saving of sticking them in the old battery spot is not worth the effort right now.