Either the mating surfaces
Either the mating surfaces are not flat or the valve cover is hitting something. The gap should be consistent and not require clamps. Make sure you get RTV around the oil passage in the timing cover or you'll mix the oil and coolant. If you can use a side looking inspection camera so see the cylinder walls, make sure there is no polishing on the sidewall of the prior bad cylinder. That means a piston rod was bent during the gasket failure. Used motor from ebay or row52.com is between 150 and 400 or so. If you can get this far with the cylinder head, there's no reason you can't pull the motor, but you might have to get an engine hoist at harbor freight or rent one.