I have a 68 Chevelle with a front mount antenna. The maximum depth of the antenna, including the antenna cable, is 2 inches - that is from the top of the fender to the point where the cowl is present.
The antenna I ordered is fine in that the antenna base will insert into the hole AOK. However, the antenna cable - which inserts into the bottom of the antenna base - does not have clearance to insert straight into the bottom of the antenna base as the cowl is right there.
I have not found an antenna that works yet... Any leads on where to get one that works?

The fender mounted three-sectioned antenna for 68 utilized a base with an integral cable, ie., the cable was molded into the bottom of the base. The eliptical mast is then threaded into/onto the base and secured with a chromed, dome-shaped nut.
There are a number of aftermarket units on ebay, and occasionally an original GM unit. Replacements with a round cross-section mast are under $20. Eliptical masts perhaps a bit more, and originals maybe a bit more still. All depends on the look you are after and what you're willing to spend.
You might try the classifieds on this site as well!
Good Luck... :thumbsup:

I think my antenna is original. The base has a little bow tie cast into it, and the bezels have the correct GM numbers on them. The cable is 8 1/2" long from the base to the 90* terminal. There was another cable from the radio that poked through the grommet on the kick panel and plugged into the cable. I've posted a poorly lighted pic of that.
Has anyone else seen the cable with the 90* end like mine has? Thanks,
BillL