Your subframe may be very similar to the one on my camaro. I had a 350 cross member and it wouldn't work with the 400, I found a 400 crossmember and it bolted right up, there ought to be one available for the Nova, it may even be the same as the camaro one. Forgot where I picked up the crossmember from but I think it was from a Chevy dealer parts counter. Been a long time since I looked at both crossmembers but I think one has the mounting bracket welded in front of the member and the other had the mounting bracket welded in back. The member is also bent for exhaust pipes to go underneath.