The recommended method to convert these disks is to upgrade the operating system to Windows 10 first, then perform the MBR to GPT conversion. So 2k8 sounds like a no no even for an offline conversion.

This disk management software can convert MBR to GPT without losing any data. Check the table to learn how EaseUS Partition master makes MBR to GPT conversion safe and worry-free: ...

I have a 2TB MBR drive w/ W7 in the 1st partition. Partitions 2 & 3 are used as separate storage. I want to xfer all of that to a 4TB GPT drive including resizing the 2nd & 3rd partitions. Most of ...

Doing so causes the GPT partition table to overwrite the data on the destination drive. To resolve this issue, the user needs to convert the GUID Partition Table disk to MBR.

The selected disk is not of the GPT partition style, then this TechNet post titled Windows Setup Installing using the MBR or GPT partition style will help you. You will have to convert MBR to GPT.

You can convert an MBR disk into a GPT disk using the Windows interface. After backing up or moving the data to a GPT disk, right-click each partition and select Delete Partition or Delete Volume.

MBR cannot easily manage drives larger than 4TB or with more than four partitions (there are workarounds, of course). GPT, on the other hand, has limits well beyond anything you’re likely to ...

This disk management software can convert MBR to GPT without losing any data. Check the table to learn how EaseUS Partition master makes MBR to GPT conversion safe and worry-free: ...