Reply to "still running warm"

To answer your question, SF, if blocked, the engine will take longer to warm up to a stable temperature- but it will eventually reach the same temp either way. That's why early-on, it was thought this made the engine run cooler.

The only advantages to blocking off the coolant bypass is -A- one less place for a water leak, and -B- if blocked off, you can run any type of thermostat, not just the special 351-C assembly. Incidentally, it's better to cap both spigots rather than routing one into the other. The lower spigot is useless in a Pantera since it restricts the adjustment of the alternator during belt changes. I pull it out & use a Loc-tited or JB-Welded freeze plug in the hole.

If the extra spigot's in good shape, keep it around. Those sheet-metal parts rust out and break so it can later be used in the upper position. If you tap the unused boss for a pipe plug, be careful. It's possible to split the pump casting if a pipe fitting is overtightened there. The crack can be TIG-welded if you're lucky. You throw away the pump if you're not....