Dean pretty much has it, as far as the perches go there's only two different widths, xk-xp and xr to fix, overall widths are different with xk-xp being the narrowest, then xr-xy, xa-el (there are some minor differences differences in widths but its less than 8mm and that's main due to the differences between drum and disc brakes) and au-fgx being the widest

what is your plan/outcome goal? 

I don't know the measurement on the spring perches, but an XR (1966) diff will bolt into a 1993 XF ute/van and the only difference being they have a different tail shaft yoke, smaller center bore on the wheels/axle and are narrower between the backing plates(over all width is narrower XR - XY)   An EL leaf spring (wagon) diff will bolt into an XF and and even down to an XA (XA and early XB had the smaller wheel center bore like XR - XY) but the diff is basically the same width as XA onwards.    AU and therefore probably BA BF FG diffs bolt into EL with the same spring perch, but the AU diff is wider. 

not sure about the XK to XP, but any leaf spring car  XR to AU etc will be basically same between the spring perch. (i think the locating hole may vary in the spring perch also)
subject to making sure, this is what i believe.   @Thom may know of any other points of interest and/or measurements even

Has anyone got diff perch/saddle measurements for various falcon, fairlane models to assist diff building and identification. All measurements in metric or imperial measured at the centre of the perch. You can also measure the side closest to the outside of the car to the inner side of the other side to give a centre measirement. Cant find anything on the net so all models would be great!

If you did have one spare, I would be incredibly grateful and would offer you some more than $10. Thanks very much Eddie youre a legend.  

From memory, that's been for sale for a few yrs now Earlier factory NON aircon XF's, didn't get the deflectors, or that rubber strip plus smaller radiator, and top metal fan shroud   I think later on, all XF's got the side deflector plastics and bigger radiator, but still no rubber strip. (aka, my 92' XF ute for ref, which has aftermarket aircon)   I see replacement door rubber seals fitted, non original spark plug leads, bonnet strut fitted upside down, wrong battery cables, along with painted over windscreen wiper bolt heads, and painted over spring clamps for the windscreen washer jet hose.

Yeah even if it is what hes describing its still not worth the price in my eyes with it being a base model xf. Still if it truly was cared for all its life why would you repaint it? 

i do wonder if any of these are particularly sought after for exporting overseas..    issues i have with this one,  where's the before photos? was it rusty? the odometer cogs stuff up, was it actually broken for 20yrs and stuck on 70,000kms still?

can't see the trim on the seat for wear, (seat cover)
can't see the floor mat for wear marks/holes (drop in floor mat pictured)
can't see the rear van floor for dents (under carpet), had it hauled bricks etc? 
pretty sure it's missing the wind deflecting panels for the radiator sides, was it in a crash?  the bonnet cable isn't run the correct path, the radiator top rubber cover isn't fitted if you look at the door striker it's got a wear gouge in it that makes the suspected hinge area of the doors look like they must be cracked. (not consistent with 70,000kms also)   $30,000 in receipts? can't see it.  @SPArKy_Dave could pick even more holes in the ad for "Period original restoration right down to the shade of tint" (they never had tint)         

Completely off topic but look at this "sweet" deal  https://www.facebook.com/marketplace/item/1655352515356760/?ref=search&referral_code=null&referral_story_type=post&tracking=browse_serp%3A48cbd7b3-f7c8-4ef4-8b68-d8ca64676bad 34k for an xf!

I did a half assed rebuild on both the rear slaves so I know they are clear of debris and the hoses seemed okay but they will be getting changed along with all the other rubber components as time goes on That's probably gonna be the go for the time being as I gotta get my fg out the door first. I get that the oil pump will be cooked but if the journals aren't gonna be too affected then I'll just bump the idle up and swap it next weekend. I do wanna do rebuild the original more of an exercise in engine work than for any practical purpose although if the bores and bearings aren't too bad I'll probably just clean all the metal out of the engine and just do a cam swap and reseal. The one going in has unknown k's but he said it was running sweet before he swapped it for a V8 and it comes with some extractors already bolted on. 

is the hole in the bleeder blocked? 
the hoses can fail and get blockages also. 
if it works, it works, but if the hoses are sus, i'd change them or at least put them on a list when the budget allows     from my understanding, the oil filter should save the crank etc, but the oil pump will be sucking all this junk up unfiltered (just the screen)  not sure of anything else,  but i'd personally stick another engine in and not even bother rebuilding the other. (assuming the replacement is any good)