360 running on 4 cylinders

That doesn't make sense----that 1/2 the cylinders would be that much colder than the others. So I don't know, start over? the basics, compression. leak down tests. Devise a backyard cylinder balance test. That is, at idle, devise a way to short one cylinder at a time and look for uneven firing or non firing cylinders. What I usually do is loosen the boots on the dist and pull the wires mostly out. Use a grounded probe and a pair of insulated fuse pullers to remove a wire and short the dist. tower. Look for uneven RPM drop.

Vacuum leak/ broke plug/ bad wire/ fouled plug, you been over-revvin it? Bent pushrod damaged valve broke spring the list goes on