I do not have a degree nor any training in fluid dynamics. Therefore, I can only respond using the figures provided by Marlin and the facts as I know them.
One would assume the Ford engineers who designed the Cleveland plate and thermostat hat DID have training and/or degrees that would allow them to professionally design and engineer the coolant bypass feature found in a Cleveland small block.
The Ford engineers certainly could have designed the system with a clearance greater or less than, according to Marlin’s posted figures, the .100” clearance design they chose. But they didn’t.
Marlin chose to re-design (in his words, “improve”) both pieces of the Cleveland bypass system to allow for a clearance of just .001”.
If just Marlin’s thermostat is installed while retaining the Ford plate, the bypass will have a clearance of .017”.
.100” OEM clearance
.017” clearance with OEM plate with Marlin’s thermostat
.001” clearance with Marlin’s plate and Marlin’s thermostat
Any of those clearances MAY perform in a satisfactory manner. Or not.
Removal of the plate is not an easy task; I have done this in the past. Removal may cause displacement of 45 year old debris. The plate is not subject to wear or deterioration. Dennis’ motor is not a bare block on an engine stand but is currently in his car. In light of these facts I would not advise him to remove the plate, as there is no need to do so.
This would leave Dennis with two clearance options :
.017” using Marlin’s redesigned hat (skirt)
.100” using an OEM-spec hat
My choice would be to retain the coolant bypass system as designed by the Ford engineers, and in order to do that I would purchase the thermostat currently offered by Tim Meyer.