temp gauge still reading hot

Thermostat ?
Although new, maybe bad ?

Hotstuff,
It may be your thermostat. I saw somewhere that the 351C requires a different thermostate that a 351W. Maybe you have the incorrect one installed. Can't remember what site I saw the details on this.

Biggest cooling system problems with the Cleveland arise from removal of the brass orifice below the thermostat, thus allowing too much coolant to recirc continuously OR the use of a Windsor thermostat instead of the Cleveland part, there's a big difference.

The inlet & outlet hoses to the 2 pass radiator are sometimes connected to the wrong radiator connections, but you seem to have that detail under control.

With the Pantera I like to fill from scratch with the t-stat removed, the heater valve wide open & fill until it won't fill any further. Then raise the rear end & continue filling until it won't fill any further, then start the engine with the rear end still in the air, radiator cap off & let it run until its warm, adding coolant to keep the swirl tank full until the coolant level is increasing (overflowing the tank) rather than decreasing. Leave it running, lower the rear end & raise the front end, let it run this way for 5 minutes or so, radiator cap still off, this allows the block to purge air. Shut it down, lower the front end, let it cool, install the thermostat & repeat. Second time around, before shutting down, fill the overflow tank & install the radiator cap. Shut down again, as the engine cools this time it will draw coolant from the overflow tank in the normal manner. Air should be gone. The overflow tank may need checking & topping off over the next 2 or 3 cycles.

If I've mentioned the obvious my intention was not to question your intelligence, just go over my fill proceedure step by step.

Here's hoping you get your problem solved soon,

George