Gzip uImage ar71xx/C-55

I am experiencing issues connecting to my Airtight C-55 via a serial-TTL connection. I am therefore trying to use the factory built-in route to load my own image (the legacy pre-built gzip uImage file does not successfully boot).

156 111.214859728 MojoNetw_94:e9:9f IntelCor_71:01:56 ARP 60 192.168.9.111 is at 00117494e99f
161 114.210155289 192.168.9.111 192.168.9.167 TFTP 78 Read Request, File: vmlinux.gz.uImage, Transfer type: octet, timeout=4

By simply running make menuconfig and make I end up, among others, with this file in my bin directory

openwrt-ar71xx-generic-uImage-lzma.bin

In order to get a gzipped file specific to my C-55 do I edit the Makefile below and replace lzma entries with gzip or do I run mkimage independently?

target/linux/ar71xx/image/Makefile