I'm posting this mainly for anyone researching about the ASUS RT-750l.
I couldn't find much information on this Wifi router, but then I found out it's the same device as ASUS RT-AC1200 V2 and probably just rebranded for different regions.
Searching the PCB ID got me to wiki page about the RT-AC1200 V2
http://en.techinfodepot.shoutwiki.com/wiki/ASUS_RT-AC1200_v2
So i checked the cpu info and amount of RAM with SSH and both are the same.
After that I also checked the firmware image downloaded directly from ASUS website and both have the exact same hash.
79cae1a37babafd975f98d8501b3eca7953cd21196a6b28be00dffdc70c42bdc RT-AC1200_V2_3.0.0.4_382_70638-gfb8b78d.trx
79cae1a37babafd975f98d8501b3eca7953cd21196a6b28be00dffdc70c42bdc RT-AC750L_3.0.0.4_382_70638-gfb8b78d.trx
I've been running OpenWRT image for the RT-AC1200 V2 on the RT-750l for a few months now and I don't have any issues. Hopefully this helps someone.