I tried to purchase an extender for the 72.  All seemed well until I took it out of the box and attempted to use it. 

Great looks and great quality to the part. It was specifically advertised to fit 68-96 so I figured it was perfect for what I need. 

The tongue end latches OK to the fixed center buckle, but the other end of the extender buckle will not latch into the retractable car side. The vendor was of no help and I returned it, losing shipping both ways.....

So back to square one - has anyone found a solution, other that taking the retractor out and a longer belt installed? I don't think you can do that - the retractor is only so big? I had all the original seat belts redone so I really dont want to mess with them. 

I got a generic extender for GM vehicles for my '75 (I don't remember where now -- I'm sure it was from one of the Corvette vendors) that worked fine.  Then later I replaced the belts with ones that were not original equipment (they do not have the GM label on the buckles), and these were longer than the originals.  The difference was about $100, for that price I could do without the specific labeling.

Yes the extender was the generic one offered by seemingly everyone. I contacted to vendor who refurbished the original belts and retractors, asking if he could "make" an extender for the belt. Has not replied yet 

What is different here and I guess there were two or more variations in the OEM buckles/tongue attachments.