67 gmc help !!!!

[Family affair]

OK !! I have a 67 with factory rear leaf springs that are in need of new bushings. The problem ? I can't find any anywhere!! None of the local parts houses have any nor can they get them. I can't find any aftermarket either. From what I have figured out a 73 appears to be the same. Any input ? Also I am doing a 4/6 drop using an 87 rear axle that I had to get me to 5 lug. I am not sure if factory rear shock frame mount location will work or will I have to relocate ? I have read some info on shock choice but still confused on length. Not sure how to calculate this. Any help is greatly appreciated. Thank you.