SS/B Barracuda project

Stefan, what you have there for a seat frame is the newer early 70s style
with the round tubing style frame.
I have never personally modified this style frame to look like the 66-69
frame myself but of course with some cutting and welding it can be done
as they are fairly close to start with.
As you have already noticed this style doesn't have the gap between the
backrest and cushion. The backrest is a little taller also.
I happen to have a customers pair of seats like the ones you have in the shop
right now so I can get you some accurate measurements of how they differ
from the earlier frames.
I have never bought any reproduction covers from Kramers or legendary to determine
which frame their covers are designed to fit. But it would make more sense they are made
to fit the 69 on back frames.
The 69 and earlier frame is not a round tube frame. It is constructed of folded flat steel.
The foam is a separate removable part from the frame on the newer tube style you have.
This will make it easier for you to modify so your covers will fit.
With the older flat steel frame this is not the case. The steel frame was placed in a mold
and foam was injected encasing the frame making the foam and steel a single part. Then to be
upholstered with the vinyl cover.
I will take some measurements and post here later today.
You need to look at your covers. The backs in particular. If they don't appear to be long enough
top to bottom by an inch or two it can be safely assumed they were made to fit the 66-69
frames. I will show you how the backrest cover will need to be fastened to the frame at the
lower gap. You will have to build this provision into your frame as it is not there on the newer
style. Not hard at all but something you need to know for the covers to fit.