Too long for a comment
My tests are too long to fit in a comment so pardon my break from tradition in posting the results in an answer. Remind me later and I'll delete this answer.
Current kernel version
$ uname -r
4.14.13-041413-generic
Look for Kernel header 4.13.0-26
$ apt list linux-headers-4.13.0-26-generic
Listing... Done
linux-headers-4.13.0-26-generic/xenial-updates,xenial-security 4.13.0-26.29~16.04.2 amd64
Install Kernel header 4.13.0-26
$ sudo apt install linux-headers-4.13.0-26-generic
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
linux-gcp-tools-4.10.0-1008 linux-gcp-tools-4.10.0-1009 linux-headers-4.10.0-38
linux-headers-4.10.0-38-generic linux-headers-4.10.0-40
linux-headers-4.10.0-40-generic linux-headers-4.4.0-101
linux-headers-4.4.0-101-generic linux-headers-4.4.0-103
linux-headers-4.4.0-103-generic linux-headers-4.4.0-98 linux-headers-4.4.0-98-generic
linux-image-4.10.0-38-generic linux-image-4.10.0-40-generic
linux-image-4.4.0-101-generic linux-image-4.4.0-103-generic
linux-image-4.4.0-98-generic linux-image-extra-4.10.0-38-generic
linux-image-extra-4.10.0-40-generic linux-image-extra-4.4.0-101-generic
linux-image-extra-4.4.0-103-generic linux-image-extra-4.4.0-98-generic
linux-signed-image-4.10.0-38-generic linux-signed-image-4.10.0-40-generic
linux-tools-4.10.0-1008-gcp linux-tools-4.10.0-1009-gcp
Use 'sudo apt autoremove' to remove them.
The following additional packages will be installed:
linux-headers-4.13.0-26
The following NEW packages will be installed:
linux-headers-4.13.0-26 linux-headers-4.13.0-26-generic
0 upgraded, 2 newly installed, 0 to remove and 34 not upgraded.
Need to get 11.4 MB of archives.
After this operation, 83.0 MB of additional disk space will be used.
Do you want to continue? [Y/n] n
Abort.
Summary
On my system at least there doesn't seem to be a problem with installing 4.13.0-26 Linux headers. However there have been many problems reported with Ubuntu LTS kernel version 4.13.0-26.