Larry,
All the Carlton built Super Courses I've seen, or looked at in via catalog specs, say they are 531 straight tubes, except Mark Bulgier's who, like me, bought his new; several years ago he reported to me that it has a double butted decal on it. Now you have found another.
Check out my "Periodic Table of the Raleigh Super
Course" at the retroraleighs site,
http://www.retroraleighs.com/
The 1978 Catalog page I have a copy of says cites "Suntour Forged", a 26.8 seatpost, and says "531 Main Tubes". Usually if butted they said so.
I sometimes wonder if they ran out of straight tube they just brazed up with butted to keep the production line running: remember the shortage of bikes back then.
Picking up the Holdsworth tomorrow!
Tom Forhan Takoma Park MD 20912
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