For 6 bolt axles on 416/ 419/ 1300, the pads are the same front and rear. if like my truck, you need 4 pads per side for front, and 2 pads per side for rear (12 total pads). Depending on source of info, there is a brass (?) shim plate at the back of each pad for the fronts (?), maybe an anti-rattle. Not near my shop/ truck or manuals, so I cannot check on this.
Obtaining pads, in UK or EU, is pretty simple, lots of sources. Next comments are based on my suspicion that you have not previously done a lot of truck mechanical work. So may be off the mark, apologies in advance. In all auto maintenance and repairs, proper diagnosis is the most fundamental and most critical aspect of any undertaking. In a MOG, that goes double, maybe triple. Diagnosis by replacement until success is usually rather costly. In my view, deciding to order brake pads before doing any looking at he situation is a really poor start. First question is, is there anything particularly wrong or troubling about the braking action ? Remember, this is not a sports car, and it doesn’t stop like one.
There are a number of threads here started by guys who have had serious brake failures, usually dragging and overheating. You should do the search, and acquaint yourself with these issues. I have been guilty in the past in not flushing and refilling the brake fluid (other trucks), and I finally bit the bullet on the Mog and did the full routine, with synthetic fluid, and very glad I did, I might add. Brake fluid adsorbs moisture over time, bad for ferrous components. Replaced the hoses to front hubs and torque tubes while open, and again, glad I did. The hoses have known issues. Pure age is the big culprit.
In your case, I would put up on stands, and check operation as it is now, specifically whether pads retract (stop dragging) when released. Then I would look at pad wear, and measure rotor thickness, to see if they can still be turned (legally, I presume laws are same in the UK?) First and last time I changed pads without turning or replacing the rotors, I barely stayed out of the ditch on the first hard stop, they pulled so badly.
Tying prior comments together, new pads change the travel range of each piston (if old ones are seriously worn), and corrosion in the previously exposed part of the bore seems to be able to affect smooth travel of the pistons after the pads are changed. This is the primary suspect for one of the Forum members BIG problems, and led to a more extensive re-do subsequently. An easy thing to check is condition of the piston dust boots. If torn, you are advised to look further, as there is probably corrosion issues within.
Lastly, when up and wheels off, you should be looking over everything else, portals are a cool but demanding mistress.
Just my thoughts, based on a lot of wrenching over a bunch of years. All FWIW