Start with a stock 1987 Trek Cirrus 520. You all know where the specs are published. You've got the following spare parts to work with:
24T chainring, 74 BCD, non-bio pace.
NOS 14-34 Z-012 Shimano freewheel.
NOS Suntour Cyclone GS
New Shimano LX RD-M531 SGS
New Uniglide 6 speed chain UG-CN51
and as head mechanic in charge, you can sell me what you've got on hand to achieve a sub 20" gear for an upcoming ride in a mountainous area in southern Appalachia
I asked this question because I thought I had it all worked out, but the LBS here in Austin, TX says...can't be done because....well, that's your quest: Can a sub 20" gear inch be achieved?