hey rob, if you do not want to machine the block, the alpha specific caps work ok. You just may need to run a locking compound that buku sells to secure the cap in place since the end of the case has a cast, tapered snout to it. Some also just use a rtv silicone.

Another option you can do to help the cap fit better without fully machining the block it to just ever so slightly machine the block to just true up the end of the block and take the high spots off (pic below) This also works ok.

But overall, the full machining of the block to fit the nova size is the best overall solution as dan posted above. The cap fits on the block very well with no distortion, and no locking agent is needed. It gives you the peice of mind that the cap will stay in place. I would highly recommend that route