I did the Caswell plating kit when I first went through my 850. It was OK, but you can't do Cadmium at home - too hazardous - so the kit is actually galvanizing, which looks like cad if you buff it a little.
I went the true clear Cadmium route when I restored my P11 and G15, and re-restored my 850. The finished product looks showroom fresh if you take a little time and clean off any paint reside, de-bur threads and clean up nicks on nuts and bolts. There are a lot of fasteners on a classic English bike, and the roughly $150 spent to replate every nut , bolt, washer, clamp, and bracket is well worth it.
3 of my bikes have the AMC primary case (similar to a MkIII case). These take 14 screws, at about $6 apiece!. Cylinder base nuts are similarly priced. that's the cost of plating everything, including items like hose clamps, spindles, and coil brackets.
I figure, cad everything, and use Stainless on stuff that's relatively cheap and showing.
My Commando has stainless spokes, at roughly $90 a rim (with good, original rims). I Cad plated my G15 and Ranger spokes, along with all the other fasteners, for roughly $150 each bike
'73 Norton 850 Commando - 3030xx
'69 Norton Ranger 750 - P11/1289xx
'67 Matchless G15CS - G15CS/1235xx
'61 Matchless G80CS - 61/G80CS/41xx