My Samurai had the repower already done, so can't comment to that - but I did strip some bits from an Escudo at pickapart - what I do know works:
Brakes:
bigger Calipers and vented disks from a LWB escudo, good upgrade to the Samurai front - and frees the disks for a rear disk conversion. Keep the front wheel studs too - they're longer than the 413 rears, and you need them if you go to a rear disk setup. The SWB escudo doesn't have vented disks, so LWB is the go if you've got one. Bigger vacuum brake booster should fit the Samurai, but you have to shave and slightly move the heater valve and very slightly open up the mounting hole on the firewall. Great with a subaru bigger master cylinder if you're really playing with braking. The power steering box makes a good upgrade for the 413, if you're going bigger tyres, some people reckon they're not strong enough, but if you've got one sitting there... And I believe if you have the Escudo lower steering shaft with the universal joints, you don't need to make up a wedge block to correct the shaft angle. I'm sure someone will correct me if that's wrong, but it seems to be how mine was done.
If your 413 doesn't have aircon, you can fit the escudo in with a bunch of work (why?), or keep the pump and go endless air (mine's halfway through...)
The Escudo radiator can be fitted, using the Escudo brackets cut down, although the 413 radiator shoudl cope if it's clean and in good nick (I'll be doing this one when I get around to it or overheat).
Longer bonnet release cable (hell wth emptying the glovebox every time you need the engine bay).
hmm - what else? Front diff ring and pinion are probably 5.125 ratio, a pair of those gives you standard gearing when running 33" tyres, so you're halfway there. I've got a pair waiting to transplant to mine, saves getting a change to lower transfer gears.
I'm using the escudo body mounts as transfer case mounts, with a bolt straight through (stronger than std transfer mounts, and won't snap off of the rubber fails).
If it's a SWB you can fit the petrol tank in (needs mounts modified) so you can get more than a few hundred k's per tank. Saves having to muck about with high-pressure fuel pumps etc too (if you're going EFI - mines carbed
)
thats a start, hopefully there's other ideas out there...
). Get him to do a package deal and get the rear brake set up too so you can swap your front calipers to the rear with the front disks and be disks all round. 
