As I've mentioned before, drive your Cobra and enjoy it. If your current engine runs flawlessly, doesn't leak and doesn't burn much, if any,
oil, then consider yourself lucky.
If you desire, then build a 2nd engine with KC, Brent, Barry, etc. that is designed as a "tried and true" complete unit. Save the money for the heads, labor and the infamous "while you're in there" cost. Combine that savings with the sale of your running engine to help defray the cost of the new engine.