Looking at my '68 PHS documents, my engine code is found on the Billing History card in box 34. These boxes match the 1968 Pontiac Accessory Groups used for ordering options, along with the price list - either factory installed or dealer installed. So for my engine, box 34 has the number 3. When I look at the Accessory Group selection, my engine is found under the heading ENGINE OPTIONS
and then under the Code
column, where I then find Code 343 (box 34 + line item 3 = 343) which is for the 350CI 2 Bbl available on body codes 233, 235, 237, & 239. Price - $105.60
Looking at the GTO engine option choices, these are in addition to the standard 350 HP engine that was part of the GTO package. So the 350HP was not an option as that was the base engine. Optional engines for '68 were Code 346 - 400 2 Bbl Reg Fuel w/Hydramatic. Price - NC (No Charge). Next, Code 348 - 400 HO. Price $76.88. It is interesting to note that the 350 HO 4 Bbl option on the Tempest, Tempest Custom, & Lemans cost $170.02, almost $100 more than the 400 HO.
My 74 is blank, but column 75 has the number "4" in it (with no explanation from PHS). On the "Options & Accessories" page, my last number on my page is 73, nothing more that tells me what the remaining 74 and up columns are. On the same page, you will see the smaller numbered boxes having "1", "2", "4", "5", etc.. These are the line item options within the Option & Accessories codes.
My educated guess is that the boxes 74 and up are Dealer-Installed Accessories. These are listed as available add-ons after the assorted factory installed options that could be ordered.
All Dealer-Installed Accessories
found & listed after the factory options use a 6-digit Package Number (Pkg. No.). Going out on a limb, I did find a "752" under Package No. 984752
and using just the three last numbers to create a 3 digit code like the factory 3 digit option codes and assuming this refers to box 75 + line 2 =752. It lists 984752 as the Left Hand Remote Control Mirror, $11.45, and .05 (1/2 hour) Dealer Labor to install. Labor was extra. If you have this, then it is a match.