Heads up is fun, but for fast cars there already is THS and XTSM275Outlaw. What about do something similar to what Pinks All Out does and let everyone run what they brung to qualify, take the avg of all the ETs, find the median/average of ET and call that the index from which all times in eliminations per racer must average out to be equal or slower. If for example the median is 7.49 and lower then race heads up, if the median is 7.50 or higher, then run an average index. I may be way off in my assumptions, but that way based on who shows up to race, the race will be geared towards that group. And a lot can happen in the 1/8th. I almost beat JD at BG in the 1/8 even though he ran 10.2 to my 10.7.
My other idea is everyone that qualifies gets 2 cards (blackjack game) and for each round you LOSE you can get another card if you want, if you WIN a round you have to stay with your 2 cards. Then once the ladder is finished, the winning black jack racer can then get one more race to challenge the ladder winner with one last showdown race heads up, no index. If the blackjack racer wins he/she gets 1st place and the ladder winner gets 2nd place. If the blackjack racer loses the showdown, then the ladder determines 1st and 2nd places.