I can bring a Stinson Voyager and formation trained pilot to the party if any good? Will match speeds well with slower GA (can maintain S&L anywhere in the range roughly 55-100kn) and with flat (and in the front, openable) windows makes for a reasonable camera ship.
Downsides are that the aeroplane's currently sick (hopefully sorted in a few weeks), the pilot (me) is a bit rusty in formation, but good enough for camera work and trying to get some more practice in this summer anyhow, plus the struts can be a mild nuisance.
G