Weak #6 cylinder

[JWL]

Yes, remove the radiator. Yes, leave the trans. Yes, remove the fan from the crank. About 6 or 8 inches will give enough clearance and twisting angle to remove. I always bailing wire or strap the trans up to maintain its position in relation to the frame before removing engine.

I don't know about a stumpfy?

Yes, those look like mushroom valves. No, those do not look like stock valve springs. Look much stronger than stock.

I would like to see the bottom of the loose tappet and the coordinating cam lobe.