Add 273's, 340's & 360's to the "318 Race" ?

Maybe do a pro-rated per cu-in system.
yeah, kind of what the penalty box does. We set a base E.T. using a pure stock 318, auto, 2.76 geared, weight of a Duster and each persons car either would either add to the E.T. or subtract, and the chart did it by item.
If you car was heavier than the base, you added a tenth per hundred. If it was lighter, you subtracted a tenth per hundred. You deducted from the base E.T. per performance upgrade (4bbl, heads, cams, overbore, gears, converters, etc etc). So a 360 block would have a certain deduction from the E.T., so really no advantage to having a bigger motor. Actually, the further away we got from the base, the harder it was to run the index.
Our winner, though, ran a 12.2 on a 12.2 index :D