I always thought the 86-87 tanks were all the same & the 88-89 tanks were the same. I learned the 86 tanks are actually different than the 87 tanks. 87 tanks share the same dimensions as the 88-89 tanks which are shorter than the 86 tank by about 1/2". The red tank I have wouldn't go far enough forward to get the bolt in on the 86 frame & the 88-89 tank I have is the same way. This is how the OEM 86 blue tank mounts, perfectly centered:

This is how the red 87 tank mounts up to the 86 frame:

Made a 3/16" spacer from kydex plastic to get the bolt in:


The only physical differences I noticed between the 2 was the length & the 86 tank has provisions for 2 rubber donuts per side on the lower section & the 87 tank has only 1 per side:

[MENTION=24]croat1[/MENTION] sent me a pic of a red tank with 2 donuts per side & [MENTION=463]Skeans1[/MENTION] said his tank was the same. I think that can be used as a quick visual reference to determine the years of the earlier tanks. Side by side you can clearly see the different lengths, 86 on the left & 87 on the right. I checked the 87 tank against the 88-89 tank I have & it's the same length:

Also Jared said the 86 tank he has on his 88 frame is opposite from the way the 87 tank mounts on the 86 frame & the bolt on his is toward the rear of the mount.