Adam, I am fairly certain that we (here on this Board) have discussed the two different VIN letters for 455 engines in 1973 Centurions ('U' and 'T', I think). Not confusing the one year only 350 cid base engine of the 1973 Centurion. So, somehow, I thought, there were more than one 455 engine produced in 1973 Centurions. I thought that the advertised 'Optional High Performnce 455' in 1973 full line brochure noted that the HP 455 engine required dual exhaust. Was there some other optional equipment combo which perhaps resulted in the HP 455 installation? And, therefore, would explain the different engine VIN digits. Indeed, your registry website has examples of 1973 Centurions with two different 455 engines by VIN (engine) digit. And, '73 being unique in that it was the only year of Centurion Production when the 350-4 was the std. engine and then any available 455 would have been optional? I wouldn't think that the VIN digit varied as between single and dual exhaust. Here's some specific 1973 examples with the apparent different engines by VIN: Example A: Cowl Tag Info: ST 73-4BP57Xxxxxxx BDY TR 448 19-19 PNT xxx ST-73 = 1973 Model Year 4 = Buick Motor Division BP = Centurion 57 = 2 Door Hardtop X = Fairfax, KS (General Motors Assembly Division) xxxxxx = Body Number TR 448 = Trim code - Black Notchback Interior 19 = Lower body color (Regal Black) 19 = Upper body color (Regal Black Painted Top) xxx = Built x week of x 197x VIN: 4P57U3X152370 4 = Buick Motor Division P = Centurion 57 = 2 Door Hardtop U = Optional 455-4 Engine with Dual Exhaust 3 = 1973 Model Year X = Fairfax, KS Assembly Plant 152370 = basic sequential production number (100001 was first built) Example B: Cowl Tag Info: ST 73-4BP57Xxxxxxx BDY TR 446 66-66 PNT xxx ST-73 = 1973 Model Year 4 = Buick Motor Division BP = Centurion 57 = 2 Door Hardtop X = Fairfax, KS (General Motors Assembly Division) xxxxxx = Body Number TR 446 = Trim code - Saddle Vinyl Notchback Interior 66 = Lower body color (Taupe) 66 = Upper body color (Taupe Painted Top) xxx = Built x week of 197x VIN: 4P57T3X196099 4 = Buick Motor Division P = Centurion 57 = 2 Door Hardtop T = Optional 455-4 Engine 3 = 1973 Model Year X = Fairfax, KS Assembly Plant 196099 = basic sequential production number (100001 was first built) Example C: Cowl Tag Info: ST 73-4BP57Cxxxxxx BDY TR 444 66-T PNT xxx ST-73 = 1973 Model Year 4 = Buick Motor Division BP = Centurion 57 = 2 Door Hardtop C = Southgate, CA (General Motors Assembly Division) xxxxxx = Body Number TR 444 = Trim code - Sandalwood Notchback Interior 66 = Lower body color (Taupe) T = Upper body color (Sandalwood Vinyl Top) xxx = Built x week of 197x VIN: 4P57U3C119236 4 = Buick Motor Division P = Centurion 57 = 2 Door Hardtop U = Optional 455-4 Engine with Dual Exhaust 3 = 1973 Model Year C = Southgate, CA Assembly Plant 119236 = basic sequential production number (100001 was first built) And, I also recall a chart of 455 cam profiles which was either put together by Denny Manner or used and referred to by Denny, but that chart showed a surprising number of different 455s in any given production year - probably due to emissions and performance tweeking .... and more thn just two 455s (std. and Stage 1) in most years.
I goofed on that...not sure what I was thinking. In 73 the VIN letter W indicates the hi perf 455. Here is the order sheet.