I may be able to acquire a PX10 - probably a 1974. It has the white paint scheme, brooks professional saddle, 531 on downtube, forks, simplex FD/RD, chrome fork/stays, and stronglight cranks. The headset, seatpost, and brakes are not original but the Duraforge MAFAC calipers are included. I"ve seen those calipers bring a lot of money on Ebay.

Is $550 delivered a fair price?

Is it a keeper or a parted flipper?

Flip. I hope to sell the brakes for $200+ (seen them sell for $500). I'd sell the bike at the vintage bike show in Leesburg. She's about 3cm too small for me.

Seems high for a flipper....

It does seem high if you're trying to make money on it. But if you do buy it, I'll buy the saddle if it's in good shape and has small rivets.

A '74 would have had an Ideale 2001 leather covered plastic saddle originally.

This seems a bit optimistic to me. The Dural Forge is a predecessor of the the Racer and a pretty commonly available brakeset. Now if they were Mafac Top-63s in NOS condition, who knows.