Restore from multiple drives to one?

Michael, restoring multiple drives to a single target would need to be approached with care as this cannot be done as a disk restore because this will always wipe the target drive first!

Assuming that your C: drive backup includes the OS and its associated hidden / system partitions, then the approach I would recommend is:

First, establish the BIOS boot mode for your PC by using the msinfo32 command and checking the value for BIOS mode shown in the right side panel.  This will be UEFI for most modern PC's or else will be either Legacy or the make of disk drive otherwise.

Next, create the Acronis Rescue Media and check that you understand how to boot your PC from this media in the correct BIOS boot mode.

See KB 65508: Acronis True Image 2021: how to create bootable media and KB 59877: Acronis True Image: how to distinguish between UEFI and Legacy BIOS boot modes of Acronis Bootable Media

Assuming that you have already made a full Disk backup of your two C: & D: drives for the next step, if not, then do this using the Windows ATI 2021 application to an external backup drive.

KB 65520: Acronis True Image 2021: how to back up files or disks

KB 65468: Acronis True Image 2021: how to back up entire computer

Note: I would recommend making separate backup images of the two drives rather than using the 'Entire PC' option which would combine these into a single image!

Shutdown the PC and remove both of the drives that are being replaced by the new drive, then install the new drive in place of the original C: drive so that it is connected to the same SATA port as that original drive. 
Note: the msinfo32 report used to identify the BIOS mode also has information to help you identify which drive is C: giving the name, size and number of partitions on the drive - this is found in the Components > Storage > Disks section.

Now with the new drive installed and the external backup drive connected, boot the PC from the Acronis Rescue Media then do a Disk level recovery of the C: drive backup image.
This will initially be resized by Acronis to fill the new target drive by default and should be allowed to do so as this can be changed later.

KB 65539: Acronis True Image 2021: How to restore your computer with WinPE-based or WinRE-based media

Check that the recovery is successful and if so, then disconnect the external backup drive and remove the rescue media, then test booting into Windows from just the recovered C: drive.

If all is OK, then download a copy of the free MiniTool Partition Wizard software and install this on your C: drive.  Launch this tool and use it to reduce the size of the C: partition to make space on the new drive to restore your D: backup to.  Note: leave the Windows Recovery partition at the end of the drive as this is where Microsoft places it!

The Partition Wizard will require rebooting the PC to perform the actual resizing of C: so allow this to go ahead and restart back into Windows again.

At this point, you can do a Partition recovery of D: to the unallocated drive space on the new drive using the Windows ATI 2021 application.  Key point here is to do this as a Partition recovery, not as a Disk level recovery!

Final comment, doing all the above recovery / resizing operations on the new disk drive will leave your original C: and D: drives untouched and safely disconnected outside the PC in case any errors are made etc.

Thanks Steve.