I was thinking about adding a few stages of drive through old transistors, and of course diodes, but then I wonder what are some more "crackly" options?
I could always intentionally misbias a transistor... but that's no fun.
The pedal also could have a vibrato circuit in it, or something to add that record type sound.
Crackling pots are a must.
Got any ideas?
I think the most old-fashioned sounds I hear on recordings tend to be various forms of speaker breakup in under-powered amps being abused. I've been listening to Blake Mills of late, and he has some delicious sounds on his recent album that are all about speaker breakup in a small amp, with no pedals doing any of the work. In his recent Guitar Player profile, he notes that he has been using an amp which is an old reworked Bell & Howell movie projector amp/speaker-cab, seen here over on the left. There is a grunt to that thing that you just can't get from a pedal.
(http://larecord.com/larwp/wp-content/gallery/sept2014_blake-mills_elrey/BLAKE%20MILLS-FIONNA%20APPLE-EL%20REY-9-18-14-12.jpg)
Bell & Howl, then?
If you want to sound like an old record, take a few ideas from here perhaps?
http://chaseblissaudio.com/warped/
Oh, and don't discount a BJT (white) noise generator mixed into your signal.
A guy here made a name for himself converting old film projectors into guitar amps.
http://www.guitarscanada.com/showthread.php?60592-Bernie-amps
And a commercial venture to replicate what he was up to.
http://www.texamplifiers.com/