I would be willing to bet the concrete in the block helped it stay together with the splayed caps not to mention your peak rpm of 7000.
I don't know being an ex drag racer myself I would've never believed a dirt track car would be so hard on parts until I heard some of the horror stories and saw some really well built stuff come apart. Part of it might be the fact that in drag racing you tune the car to peak power (shift point and rpm at the end of the track) so the motor rarely sees rpm past the power peak. Circle track cars see rpm past peak power every lap because every track usually has a pretty big swing over the course of a night between high traction and no traction so the car has to be able to pull hard when the traction is there and yet not be prone to blowing the tires off when the traction goes away.
I would say that if I was buiding a motor to put in a drag car i wouldn't be nearly as scared to build it using the block I have unless I was going to be putting a lot of spray to it.