I am helping my brother with his 70 Nova and we need to lower the car 2" , but we are not sure if the lowering blocks are permited at tracks ,any one knows if they are permitted or not?

I've run am much as 4" lowering blocks on an S-10 and never had an inspector say anything. I currently am using drop leaves and 3" steel blocks on my Blazer. I'd stay away from aluminum blocks though. I've broken more than my fair share and have seen the destruction that can happen when your pumpkin rips through the floor and wrecks a $500 driveshaft.

The track won't care. Nothing in the NHRA rules about it.
2" is a fair amount. Is the rear set up for multi leaf or mono leaf springs? Multi leaf rears have deeper spring perches.
Just make sure you use good quality 1/2" U-Bolts, 2 per side and you should be ok.

Ron