I know that there are metal holley dashpots. Not sure which one you would need. Go to ebay. As far as the spring, when I had the single four barrel it had a dual spring set up that was pretty stiff.
Jeff's sadistic answer sure got a laugh out of me. Jeff, what would we do without you.
I didn't realize the dashpots were so expensive. Before I would worry about the spring issue, and you check if pushing back on the throttle to the dashpot works? Best of luck. Larry