The Ford 300 six is a work engine. Forklifts, pickups, irrigation pumps, generators. Seven main bearings, a gear-driven camshaft, and a cylinder head that was never designed to flow air.
That head is the ceiling. Everything about the 300 is strong enough for far more power than the head will ever feed it.
So somebody worked out how to replace it with something Ford never built.
A Boss 302 head covers four cylinders and carries the canted valve layout developed for the Cleveland engine, which is the best breathing design Ford produced in that era. Cut sections out of those heads, line six of them up, weld them into one piece, and you have a straight six head with Cleveland ports on it.
The hard part is the welding. Cast iron moves when it gets hot, and a head that warps is scrap. The ones built in the early seventies were credited to CJ Batten, and the technique never really stopped. Later versions of the same idea have used Yates heads and even LS heads on the same block.
This particular engine is credited to Sherman Sligh and is known as the Boss 300. The block is bored seventy thousandths over, which works out at close to 310 cubic inches. Inside are a billet steel crankshaft, forged pistons, titanium valves and 13 to 1 compression, fed by Enderle mechanical injection.
Six hundred and twenty five horsepower, naturally aspirated, from a straight six.
That is over two horsepower per cubic inch with no turbocharger and no supercharger, out of an engine family that spent most of its life running water pumps.
The claim that it set an NHRA Competition Eliminator record in 1970 gets repeated a lot. The parts in it suggest a much more recent build, so treat the date carefully.