Technically these were HP heads if you include the valve train. I recall reading that Denny Manner confirmed these do not include the swirl polished valves like stage 1 heads.
The 71/72 code TA/WA GS 455 had larger valves then the standard Riviera TR/WF 455's - - But were not referred to as Stage 1 by GM. the option was A9 Riviera GS Option (Includes Firm Ride And Handling Suspension - Performance Axle - Positive Traction Differential - Whitewall Tires - Chrome Plated Air Cleaner - Modified 4 Bbl. High Performance Engine & Specific Ornamentation) 1973 XA code 455 - (could be ordered with or without GS package) and was the same as the previous two years "A" codes. and was option A1(Stage 1) Option - High performance 455 cu. in. 4 bbl. V-8 engine. Matched THM 400 Performance axle with positive traction. chrome plated air cleaner. Stage I name plate on grill. (this was the only year GM used Stage 1 to to the Riviera 455 engine which was the same valve size /valve springs/cam etc as 71/72 Riviera GS 455. and the GS package was just [TABLE="class: main"] <tbody>[TR="bgcolor: #f1f1f1"] [/TR] [TR="bgcolor: #f1f1f1"] [TD] [/TD] [TD]A9[/TD] [TD]Riviera GS Ride and Handling Package - HR 78-15 steel belted radial ply whitewall tires. Specific springs and shocks. H.D. stabilizer bars. H.D. wheels. Specific insulation package. Specific body mount system. GS name plates on fenders. [/TD] [/TR] </tbody>[/TABLE] Non of the above Riviera engines are the same as A body "S' code Stage1 - which not put in any Riviera - remember that one the main definitions of a Muscle car - is a high performance version of a full size engine - in an stripped down lighter weight intermediate body - thats how it worked at Buick (except for the stripped down part) [FONT="]. in fact if you look at HP ratings you'll find the A body GS 455 engine matches the base Riviera 455. 315 hp A body GS Stage 1 and Centurion HD 455 (big valves - higher lift cam than[/FONT][FONT="]1384664[/FONT][FONT="]) 345hp[/FONT][FONT="] - Riviera GS 455's 330 hp[/FONT] [FONT="][/FONT] [FONT="]So yes Technically the 71/72 Riviera GS "Stage !" and Centurion 455 Heavy Duty was not refereed as Stage !, just Riviera GS, or Centurion HD. and the only way to know for sure is to have documentation and.or remove the heads. ( I once owned a 70 Estate Wagon - that had the Stage ! heads) The Riviera GS/Stage 1 engine and the Skylark GS Stage 1 both used 1/8" oversize intake and exhaust valves. While the Riviera GS(71/72)/Stage 1(73) engine had its own cam with more lift than a standard Riv 455, giving more low end power (Riv GS Camshaft pn - 1384664) the A Body Skylark GS/Stage 1 camshaft had significantly more duration for more top end power. Supposedly the A body cam, was deemed to run the engine to rough for use in a Riviera , The Rivs did use the heavy valve springs, also Riviera GS did not use the special carb jetting , distrib, deep sump fuel pump the A bodies did - [/FONT]<!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <woNotOptimizeForBrowser/> </w:WordDocument> </xml><![endif]-->[FONT="]71 Riv GS Camshaft pn - 1384664 Intake Duration - 297 deg Lift - .410 Exhaust Duration -322 deg. Lift - .457[/FONT] while on the subject of clearing up misconceptions that have been going on very long time <!--[if gte mso 9]><xml> <w:WordDocument> <w:View>Normal</w:View> <w:Zoom>0</w:Zoom> <woNotOptimizeForBrowser/> </w:WordDocument> </xml><![endif]-->[FONT="]he GS or Stage 1 packages had nothing to do with the interior, many people seem to think the bucket seat and console make their car a GS[/FONT]
