I have serpentine belts on my 68 RR too,
I bought individual pulleys that fit my need
from March Industries, got them from Magnum Force Racing,
I have an electric water pump {& fans} only run an alternator & a power-steering pump,
I made a idler bracket out of a 1/4" piece of 7071 Alum.
I mounted it off the water-pump front top right & got the idler pulley from MFR too..
I didn't like the looks & bulk of the kits & 1 belt designs,
I had to do some shimming & altered spacers off the alt. &
for the power steering to line up, the Pro-Sport 7-1/4' billet steel damper {Mancini Racing},
I would have had to do custom shims either way, it's a weird thickness...
I like it much better, it's far lighter, no power loss, really quick rev.'s & no belt throwing,
IMO much better than the V-grove OE stuff too...
Simple easy deal, not a big heavy expensive
{I don't care about price usually unless it doesn't add any performance benefits}
& really fugly/bulky bracket hanging off the front too...
If I am to replace something, I want something better & performance oriented...LOL
sorry about the photos they are really old & they suck,
but only ones I have at the moment...
wasn't planning on really sharing them