Great Photos and a very colorful LT5 for sure
I am not sure why you did not just block off TB coolant with a 1/8 inch Allen Head Pipe plug (same with IH housing and Plenum TB coolant path). That would eliminate having to draw down coolant every time you remove the Plenum which I just know will be whenever you get the urge
I defined a great Coolant Filling technique which has eliminated the fear of Water Pump Air Locking after a Coolant Refill.
Are you uncertain of TB Icing? Just am interested in your opinion leading to your modifications.
Thanks,
Cliff