With the successful scavenging of these four Ace Doubles, I've finally reached a milestone in my obsessive collecting.
With G-623 (second from the right) (Philip E. High's These Savage Futurians & John Rackham's The Double Invaders), I've finished off the G series.
Only 14 of the 200+ Ace Doubles were published in the G series, so this isn't a huge milestone. But, I finally have a neatly arranged row of ticks on my checklist. And I can officially declare that shelf complete.
But I'm close with the F's (31 of 38), the H's (18 of 19) and the M's (18 of 19). The countless D's and the 'Numbered' series to follow. Then after that... westerns and mysteries, of course!