how to answer “Device for boot loader installation” query for 2-linux/2-drive setup

I have a Dell Precision 5820 with 2 of a possible 6 internal HDs installed. The first came with a factory-installed (and barely-supported) Ubuntu 16.04 on board. Of course, with the Radeon graphics card and a Dell freeze before its drivers were available, that made the linux kernel upgrade from 4.x to 5.x necessary. That eliminated the notorious “login loop” plaguing AMD and NVIDIA boots. That done, I’m adding Ubuntu 19.04 which is supposed to be integrated with the new kernel and drivers. Smoothness is needed every once in a while.

The first drive contains three partitions: sda1 (EFI System; fat32; boot/esp), sda2 (Basic data; fat32; msfidata); sda3 (ext4; Linux filesystem). I partitioned the second 1TB drive with the equivalents of the first hard drives’ sda2 and sda3 partitions: there is no equivalent of sda1 partition. The install location for Ubuntu 19.04 (label=OS; type=Basic data ; contents=fat32) and the accompanying filer’s area (label=UBUNTU; type=Linux filesystem; contents=ext4).

I am stuck at where the 19.04 installation asks where to install the boot loader. I thought I’d be asked about an N-boot possibility, and thus, to defer to the sda MBR location for the grub (v2.0.2) boot loader, running an admin tool that auto-modifies grub to “see” the added OS, so it can display that option in its user ‘start-up’ menu.

Grub apparently only needs to be in the MBR of drive 1, even though I’ve seen sites discussing having it on each drive. So, I am wondering if selecting the default sdb1 location will “update” that Grub-set to “see” both OSs… without breaking the running Ubuntu 16.04.3 on the first drive.

Thanks in advance, “frank”