Dennis,

I agree with jamesc that the low gearset wouldn't be the best place to put 400 at this point, but more info is needed to decide where to put it.

Is 10.5 as wide a tire as the car can handle?
"Old Indy's" Are they -1s or SRs??
What broke on the motor?
What cam is in it?

If it's a 440 with -1 heads, the combination of converter and camshaft are key. Typically less duration will allow for more torque in the usuable launch rpm.