I am not at all surprised that you pulled a 2 pin one out of the front...
My front one had never been out before (I could tell by how much swearing was involved getting the hubs apart... far more than the steering box!) and is a very late production model from what I gather (Jan 2001) and it only had a 2 pin in the front... A lot of the naysayers who stuck to the line that 4 pin was shipped in the front of the later ones couldn't really believe it - but it was definitely 2 pin...
I do have a 4 pin rear diff in the front of mine, and I honestly don't notice any more noise from it than before I had fitted it. Most of the whine in mine is from the transmission. I struck out, as I got a very low mileage 4pin diff which was going to go in the back, and then I was going to sort the front out at some point when i had time - but then I won an auction for a never-used 4 pin rear diff, so chucked that in the back in place of the worn 4pin that was there, and put the low mileage 4 pin one in the front...
I need to give the diff oils a change at some point, so will see what the state of the fluid is that comes out of the front... if there aren't massive amounts of shavings or chunks of metal, then I'm going to assume that even though it is running in reverse the whole time, it's not actually wearing any quicker... if it is wearing quicker... well, I'll cross that bridge when I get to it!
'06 4.2 Supercharged Black/Cream "Jess" -- Bought April 2021 (NZ)
'01 4.6 Vogue Black/Lightstone "Snog" -- Bought Jan 2012
'99 4.6 HSE Cobar Blue/Lightstone -- Sold March 2009
'95 4.6 HSE Epsom Green/Tan -- Traded June 2008