I'm trying to find an exhaust leak and I've stumbled upon discussions about seafoam cleaning engines and producing lots of smoke. I figured I can kill 2 birds with one stone. Popular choice seems to be 1/3 fuel tank, 1/3 crankcase, and 1/3 can into intake. Is this safe to try in 66 with stock 289? It seems most threads I read were dealing with fuel injected vehicles. Which is the best vacuum hose to use? And finally is it necessary to change oil afterwards? Thanks in advance.