Big Block spool mount motor mounts

In my opinion $80-100 for the pair. There's not a huge market, but I'm not sure how many sets are still out there. Replacement isolators are pretty poor quality these days. I had an old pair on the shelf that I installed on my mounts, but the fit is terrible. I just put a few welds on to hold them in place. That should be fine for the life of my car. Poly inserts are also available.
Does the K frame modification and these spool mounts work for a 383 or is it just for a 400/440?