Hi Hondu. Just yesterday I had a look at a 91 model 75 in the very hot sun, so hot that I could not climb under it but I stuck my phone under it and took some videos, including one under the left side from the drivers perspective front wheelwell and saw this:
Apologies for the quality of the screengrab--the rest of the numbers are there. When you say it is a no numbers truck, I just didn't understand. Not criticizing or anything, just was hoping you could clarify. I should hasten to add that my 2001 rust bucket late night beer-induced ebay mistake (which we somewhat affectionately named 'Crusty' is so rusty that the frame number probably can't be read.
The frame number is on the passenger side either in front of or behind the front tire, depending on land cruiser model. They may be in multiple places but this location is always easy to see.
Here’s a pic from my 1994 FZJ75. It’s behind the tire between the exhaust pipe and the shock tower. Should be one in the same location on that 1991.