Been running a W58 box in my ute for the past 9 years, never had any problems with it been tooo big.
Have 3 mates running the same, and know of at least another dozen running W50, W57 and W58 boxes.
If ya don't want to change bellhousing, just make a template up of both mating surfaces and then get some 10mm plate and then take it past ya local laser-cut shop anf have it fabbed.

Go and have a look at streetfire.net and type "Nissan 1400" into the search block on the top of the page, brings up a cool drag run between two utes with 4AGE powerplants in 'em having a go at Wesbank Raceway in South Africa.

Check out http://www.hotrodsandhemis.com/Traction.html and http://www.calvertracing.com
I copied the first sites instructions when I made mine for my ute. I went and bought 4 chromoly rose joints from the local bearing shop and inside threaded two half-inch steam pipe sections and they worked beaut.

Heres a link to a site with details on the Alfa diff tht I have been using from a late eighties Alfa Berlina 4,3:1 ratio. You also get em in 4,11 & 4,54 & 3,9. Check the local Alfa Club, maybe there are some lying about.
http://www.alfamilano.com/articles/lsd/alfa_lsd_rebuild.html
By the way, the diff housing/casing is partly aluminium but I can assure you the bearing carriers are definitely not. From all reports, they seem to handle up to 500Nm of wheel torque before they pop - remember its torque that kills drivetrain parts, not kilowatts.

I'm here too.... in Willetton....newby to Perth still finding me way around

absolutely right, kulula, leaving SA end of this month, painful to part with bluuey - had him for 8 years now. Pulling the Mazda motor and crating it cause we've got the recipe for power just right. Personal best still at 11,01 @ 217kmh on unprepped track with only 259KW@1.5bar ATW. We've had "issues"with drag events here recently, so I've run out of time to try and better it. Running close to 400kw now, without nitrous, just over with the nitrous on - but pleased that we've got it to go so sweet now!

Carbon fibre bonnet, 15 inch 6,5j FRONT and 8,5j REAR Jazz alloys, Caltrac bars, over diff rear stabilizer setup, Alfa 4,3 LSD, cressida 5 speed box, full interior with formula design buckets/harnesses, e-boost controller, fuel cell, large bosch fuel pump, tonneau cover, 10 inch M/T slicks for track, Bilstein rear full adj. gas shox, Koni front struts SPA1 90/10 drag setup,BMW 290mm discs with 4-pot calipers, intercooler, radiator,shift light, battery & housing, towing A-frame and rear tow board. R30 000 or nearest offer, pics in my profile, PM me if interested. Only thing missing is the engine & management system.

Have any of you fellas imported a complete engine into Aus recently (second hand /pre-owned/purpose built/drag motor/not for street use). Battling to find any decent info from customs - they just sprout loads of info concerning whole vehicles. Any advice would be appreciated

Have to sell her, leaving the country:
1990 Nissan 1400 ute/bakkie
Mazda 2litre FE3 motor
T4 Garrett Turbo, Nitrous oxide (small 1 fogger kit), Custom louis lima cams, big valv head, steel crank, Wiseco pistons, Crower custom rods, Koni SPA1 drag coil-overs/insert front, Bilstein dampers rear, adjustable Caltrac bars, adjustable rear stabilizer bars, MSD ignition, Domingos f200 Fuel computer, street rims Jazz alloy 6J front 8J rear, race rims Spin Werkes light weight 3,5J front 10 J rear, RC 1000cc injectors, complete Aeromotive fuel system,cressida 5 spd box, 2 plate clutch - Clutchmasters, Quartermaster hydraulic throw-out clutch actuator, LS diff Alfa 4.54, e-boost and lots other guages, MSD NOS rpm actuator, R88 500-00 complete or rolling chassis with gearbox R40 000-00 - check my other posted photos for pics.

http://datsun1200.com/modules/myalbum/photo.php?lid=16951

Heres a pic with the 26/8,5x15s, just had the flares done, but didn't need actually need them with these tyres