Some notes:

Reynolds was drawn to SWG despite being in Birmingham.
See "Top Tubes" brochure:
Reynolds "Top Tubes" booklet (10-1977)

According to Reynolds "531 professional is the direct replacement for the former 531SL"
See 7:58:

531SL was definitely the same gauge as 531pro/753R in the main tubes at least
See bulgier's site for specs:
p10_531_SL.jpg

531 "sprint" is equivalent to Super Tourist, not 531ST(special tourist). This is confusing and even modern Reynolds gets it wrong in their decal history pdf.
See "Top Tubes" brochure:
http://www.equusbicycle.com/bike/rey...80brochure.jpg
See 9:07:

Some of this info is also found in Paterek's tubing chart that was previously posted.