Actually, scratch that...
In Australia the Omega is the base model Commodore...
Numbers work well...
Using the tradional trim levels of L, GL, GLS, CD, CDX, Sport/SX, Elite and add in Exquisite and Platinum, give each a number from 1-9.
Models can be renamed too... Viva 1; Adam 2; Corsa 3; Meriva 4; Astra 5; Mokka 6; Zafira 7; Insignia 8; Cascada 9; Omega equivalent 10.
Decimal points being used to define the trim: .1 being the base designation and .9 being the highest. So a GLS would be 10.3, the Elite 10.7 and the Platinum 10.9.
Taking that one step further you could also define the engine in the same way... so a 2 litre 4 pot GLS could be 10.3204 and the 3.6 Platinum could 10.9366.
Works across the range... Base model Viva would be 1.1103. Base Astra would be 5.1144 and so on.
Room in the designation for a 10 model range, each with 9 trim levels and say a $4,000 spread between the base .1 trim and the .9 on any model. Make the specs identical across the board. And price the cars simply... say start the 1.1 at $5,000 and make each model $2,000 more expensive. This would effectively make the base 5.1(Astra) $13,000 with the 5.9 being $17,000. The range topper 10.1 would start at $23,000, with the 10.9 being $27,000.
Basic price would include the smallest current engine with a surcharge of $1 per cc, so a 1.3 would come as standard with the 1 litre 3 pot, but could be available with the 1.4 four pot, demanding a surcharge of $400. Auto box would be a $500 option where available for any given engine. Likewise four wheel drive.
Base engines being defined by the smallest engine available for any given model. The largest engine option for each model being the same, so the 1 might only be available with the 1.6 4 cylinder as its largest option.
Body styles would be hatch, saloon and estate. Five door hatch being standard. 3 door would be a $500 option, 4 door saloon would be an NCO, and estate would be a $500 option. For the 10 a two door coupe could be offered at a $2,000 premium.
Notable exceptions would see the 2 as a three door hatch only; the 1, 4, 6 and 7 as a five door hatch only; the 9 as a two door convertible only; and the 10 as a saloon, estate and coupe.
The Camaro, Corvette and Suburban derivatives would remain unaffected as they're effectively standalone models.
The crux being that globally anyone should have access to any model in any trim without penalty and the only options trim level, colour (body and interior), drivetrain and body style. No other options... if you want a 1 with heated memory nappa leather and touchscreen nav and xenons and the basic engine, then you buy a 1.9103 for $9,000. equally if you want a large family estate with a large engine, autobox and four wheeldrive on a budget then you would order a 10.1366 for $26,100... ($23,000 basic plus $1,600 to upgrade from the two litre four pot to the three.six v6, plus $500 for each of estate/auto/4x4.
The range topping car would be a 10.9366C 4x4 auto at $31,600.