Big block cooling issues

Agree on put the thermostat back in.
Agree ditch the 10" fans.

IMHO get a 7 blade OEM fan, space it an inch from the radiator, NO shroud, and see how things go.

Any shroud that is flat will build up pressure at speed and you will have reduced cooling at speed, OEM shrouds have HUGE openings for the fan/ fans and are tapered like a funnel.