Thanks guys, I may have a more serious (or simply frame specific) set-up issue then. With the 15-28 freewheel installed the B screw is wound out so far it can only be hanging on by a couple of threads, I'm worried it might bend or drop out. I have experimented with chain length and in this configuration (53/39, 15/28) I can't quite strike the right balance, it's either too short for the big gears, or too long for the small gears. I can of course avoid the situation of a long chain by not riding 39/15 so easily sorted.
The main issue is the poor indexing due to the distance between the top jockey wheel and each subsequent sprocket. Campagnolo's 1987 Record brochure extols the virtue of the derailleur design which moves in a perfect perpendicular movement and then in the 1988 Athena & Chorus literature they are shouting about how the skewed paralellogram maintains a perfect and uniform distance under each sprocket for perfect shifting..what a difference a year makes!
I went out this morning with the Athena RD from my other bike, I think this is possibly the way to go, I had considered buying Croce D'Aune but you try finding an Syncro index insert for it!
1989 Raleigh 531C Race
1990 Raleigh Dynatech Castorama replica
1991 Raleigh Dynatech Lo Pro TT
2012 Raleigh Airlite Campagnolo Centaur 10 speed
2013 CYFAC Proxidium Campag Athena 11 Speed
2013 Team Europcar Colnago C59 KoM edition