Those are '90/'91 454SS seats.
'92/'93 454SS's have these...
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I will build upon my last post;
I will not say that I know with clarity if 1990 style buckets were used in 1991, but default to my buddy's knowledge citing that the 1990 454SS seats were specific...
Maybe someone here has a 1991 full model brochure?
I recently bought both versions of the 1992 (USA market) truck brochures, as well as the sales book;
Although my literature is one model year newer than your truck, it should at least help suggest what
might be correct for your truck.
My smaller brochure (24 pages including rear cover; light paper covers) only shows the 454SS interior on page 7;
My larger brochure (68 pages including rear cover; heavy paper covers) shows a LOT more about the 454SS - this brochure is the main reason why I am making this second post;
Page 24/25 has a nice two page spread showing the red interior in an extended cab silverado with the "optional reclining high back bucket seats" - those EXACT same (inside armrest only) seats are shown also on page 21 - pages 20 & 21 are a two page spread on the 454SS model, and page 21 has a nice (albeit smaller) picture of the 454SS interior - with those same single (inside only) armrest seats.
The larger brochure does clearly spell out paint availability, but does not spell out interior colour options;
I know that 'garnet' red is generally affiliated with the 454SS, but had thought I had seen the odd one which did not have a red interior.
My interpretation of this brochure is that any 'silverado' cloth interior could be ordered with the 454SS as long as it aligned with the colour chart;
If youre truck is in fair condition, the RPO sticker should be in the glove box - hopefully it's readable - if not, any GM dealership should be able to get you the full RPO list at your request (the RPO's will tell you the original colour and seat configuration for your interior).
Back to the bigger brochure - Paint colour options are clearly spelled out on page 37, and again on the colour chart on page 33;
Page 37 under the 454SS 'Interior Features' category, does NOT say that only red was available.
If I was never able to buy my grandfathers 1992 "Sport" truck, I would have been gunning for a 454SS...