thought 411s had h165s with small axles

The P411 used an alloy carrier version of the H165 in the 'rear' diff [to distinguish if from any other diff a 1200 might have]
These will bolt into the 1200 Ute rear axle housing [which is not readily available in Washington state] They will also bolt into the PB110 & PB210 Excellent rear axle housing [from which the ute rear end seems to have been derived] Unfortunately there are not readily available in the US either.

These earlier diffs use a different spline in the side gears & are a 4.11 to 1 ratio.

Simply put, the early [alloy carrier] H165 differential will not fit either the H145 or H150 axle housing & even if you had the correct housing to use it in, the 1200 axles will not plug in.

It may be possible to rebuild it with the later side gears from the [iron carrier] H165B but you will still need a suitable axle housing for it.
I also think it will not serve you too or too long well if you continue to dish out the level of abuse that you describe.

May have to bite the bullet and have a 720 diff shortened up for it. in the long run a properly strong diff is the only way to go. Shagging about changing heads is only shifting deck chairs on the titanic when you have lots of grunt and a heavy foot.

Well, broke the left axle shaft inside the bearings on the pumkin. I guess that's the reason why it never broke loose and rattle inside my rear diff. Replace the bearing and axle and it's fixed but I'm not going to go that route. Think I'll pick up something a bit beefy'r.

Are H150, H165 or H190 the same width, drum to drum? How about the drive shaft bolt up pattern?
I want to make the swap over as simple as possible.
Thanks.

just try not to get a monster huge diff that is way to heavy for a small car. my car has a torana diff in it which would weigh about 90kg's and you can feel it just pushing the car around and making it understeer.

irrelevant. This car only goes forward, no need to turn right or left

Dman, thanks for that info. It never occurred to me that the ute rear axle and Datsun Competition axle housing is straight from the PB110. It makes sense.