Windows 10 build with tangled HDD allocations  

Running Windows 10 pro V.1909 OS build 18363.657. The PC was home built using a M5A78L-M PLUS USB3 mother board that does not support UEFI. Drives are 256GB SSD, 1000GB HDD and 2000GB. The two HDDs are from from a previous win 7 system.
As it stands now the system takes 2 minutes to boot and it does so off C:. I suspect it has to do with the way the dives are set up.
See the attached screen shots.

One thing I now realize is that I should not have deleted the win 7 OS from G:. How to fix the MBR?
Why does D: show empty in file explorer (I did move all the data off it with cut/paste) yet This PC shows only 132MB free of 578?
What is the significance of Disk 1 being GBT?
I am hoping to have only the OS on the SSD in a single partition.
Any help to climb out of this mess will be much appreciated.

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In addition the BIOS boot sequence is set to DVD, SSD and USB. It's amazing it boots at all!

Yep. Your system is definitely a mess. It is booting from disk 2 partition 1 which is G: drive.