"where can I get a 1520 movement for $650?"
NOT on the internet. Bought another 1520 since the 5513 project...544xxxx serial number AK 5500 for $775 with a 1972 dated C&I/rolex signed rivet oyster, all in 85% condition, way too nice to part out. It looks like it never has been worked on, all screw heads and plates are unmarked, no flop in the rotor axle, probably been in a drawer for years. I got it at a local flea market.
Bought a 20mm C&I/rolex signed jubilee and a 20mm C&I/rolex signed rivet oyster last week, $100 for the pair...another flea market find.
Bought an AK 14010M with 13 link oyster in 90%+ condition just before Christmas for $1000 from a guy needing $$. This is the 16th 14000/14010/14000M/14010M AK for this price in the past 10 years...about half of them unworn in box (presentation watches).
You gotta shake 'em outta the bushes.