Don't have a DIY macro rig yet, but I just picked up a Minolta Bellows 1 in mint condition for $25.
I know I can use the macro rail (the lower one in the photo below).
About the bellows, I'm not sure what to do yet:
1. Replace the mounts at the ends to attach to Pentax camera and to take pK-mount lenses. I have a cheapo pK-mount 3X TC that can act as organ donor.
2. Or I can just buy glassless Pentax-Minolta and Minolta-Pentax adapters.
3. Get a Minolta (lens)-to-Pentax (body) and buy a Minolta lens to dedicate to this rig (frankly, I'm not too crazy about this).
4. Sell it.
Have any of you done this before?