Ok, I prototyped this (yay radio shack electronics labs :) with two
0.01u/100k oscillators, each buffered, using up the hex inverter.
The outputs went to D and C of the D flip flop, resulting in the
oscillators changing too fast for the eye to see but the FF changing
about 2-3 times a second.
More fun: I replaced the D-FF with a pair of XOR gates (dual xor
available in US8 package); one wired to show "in phase" and one for
"out of phase". The two LEDs kind of "throb" back in forth, instead
of blinking (because when they're 90 degrees out of phase, both LEDs
are on 50% of the time, etc).