had a good look at the diff in my '74 1200 ute today, and its a borg warner. This is different to the H165 & H145 diffs right? as far as i can see (from the tech section) i think its a 120y diff... would this be right? If it is would this diff be strong enough to handle a L20 engine, with extractors and a weber? otherwise i gotta start collecting diffs...

What is it about the diff that suggests it is a Borg Warner?

do you mean it is a salsbury type

Hmm ... salisbury type has the gears inside the axle assembly. The Nissan/Hitachi type has a removable gear assembly (third-member or "pumpkin" or "head") just like a 9" Ford only a wee bit smaller.

I know its a borg warner because its written on the bottom... (!) is the salsbury type the one that the back cover unbolts as a pose to the front of the diff unbolting? This one unbolts on the rear

Sounds like you will need to start collecting diffs. In my experience, borg warner diffs are complete peices of sh1t. (Although I've never had one in a datsun)

i've been running an old, very rumbly, 120Y sedan diff. it's the biggest borgwarner i could find. Anyway it's been rumbling away for years, 4 or 5 of them have been behind my Mild A15.
I'm not much of a burn out man but it does cop plenty of full power launches and it's still going strong.
Even this mild A15 is still a pretty low torque kind of engine compared with larger capacity donks so most of the running gear should be pretty low stressed i reckon.

The whole point is that i reckon unless your expecting massive power/torque increases from your L20 i "reckon" you'll be OK.
My A15 only puts out just over 60HP at the rear though. Can't recall the torque figures.
Ute diffs are fairly pricey these days. Does $400 -$600 sound about right? If you can get one!
However getting a propshaft made up to join the L-series box with your diff will cost a fair bit too. If you break diffs and have to change to a ute diff later on you may have to get your shaft modified again!

Also there are the ratio aspects to think of. The ute diff will let your motor spin up fast. Good for A-series engines not destined for the freeway but your L series should have the torque to justify a lower ratio diff....like the 120Y diff in there now?

I'm interested to hear what you do.

the tailshaft should't be a problem, i got one that fits both ends, just need to get it shortened... I think i'll leave the diff as is and see how it goes, when it breaks, i'll find something else...

I bought the L20 off a guy who had it in a 1200 ute, except he had a shortened holden banjo diff... he kept snapping axles though (they're never as strong when u re-weld them) now he's upgraded to some other nissan engine, (forget what exactly) its complete with turbo, wolf computer, ect.etc. he's got a gearbox from a 302 v8 behind it i think. I'll have to get his diff, coz it won't be strong enough for his car anyway...