Have a 1967 250S with a 6cyl overhead cam engine. The engine is seized from sitting for 25 years . I've soaked the cylinders with kroil for 3 weeks and it wont budge. Crank damper nut wont move.

How do I safely remove the cylinder head to take a look and maybe tap the pistons. Cant turn the engine to get at TDC. Will I just have to cut the timing chain and then reset everything once I get the engine moving?

Thanks