put MBR on GPT disk, bios machine

Hello,

Background, I have a 2008 era bios-based machine that I want to upgrade/replace. It has a 500g drive.
I'm hoping to do it in two phases
1) upgrade the disk, install a 64bit linux on it,
2) move the new disk into a new UEFI box later.

I installed a 4TB drive and installed 64bit 12.04 successfully on it, with one issue, that it still
boots off the 500g drive. The 4TB disk as a 1G /boot partion, and the remainder is a LVM
paritiion, divided into
- 16g swap encrypted
- 25g root
- 30g to install 16.04 later
- remainder user data, encrypted
The fstab it generated is below.
It all worked fine, except that the MBR/grub stuff went onto the 500g disk. I.e., it only boots
if the 500g disk is first, otherwise it hangs at boot. I want to be able to boot from the 4TB disk
using the current 2008 bios-based machine, and also later boot from it using a UEFI machine.

My question: is it possible to put a MBR and grub onto the new 4TB disk?
It has a generous 1G /boot partition that could be deleted and divided up
to make room (I read something about grub stage 1.5, but do not understand).

I am a programmer, but not a linux or hardware expert, please keep your reply (if any) on the simple side!

# <file system> <mount point> <type> <options> <dump> <pass>
proc /proc proc nodev,noexec,nosuid 0 0
/dev/mapper/wobblygroup-root / ext4 errors=remount-ro 0 1
/dev/mapper/wobblygroup-rootB /Futurelinux ext4 defaults 0 2
/dev/mapper/wobblygroup-unused /Unused ext4 defaults 0 2
/dev/mapper/wobblygroup-home_crypt /Users/zilla/zilla ext4 defaults 0 2
# /boot was on /dev/sdb1 during installation
UUID=4a096c2f-ff47-449d-b744-b37de1e0ef13 /boot ext4 defaults 0 2
/dev/mapper/wobblygroup-swap_crypt none swap sw