I have an H145 4.4 diff in an alloy carrier (1000 wagon) and wish to put the crownwheel and pinion in the H145 3.9 cast iron carrier (1200 sedan) for added strength.
I have had some differing opinions about this being possible or not so I am asking if anyone here has done it before and with what degree of success.

shoud be a straight swap but the cast iron carrier is 10 kg heavier.

roger that, straight swap. tho i did it the other way around to save weight. you can put any old 145 centre in the carrier. so you could have an alloy 3.9 or 4.4. if you need an iron carrier for more strength then i think you might need a new bigger diff altogether. go the alloy!

Sidey just save up for a Winters speedway diff the complete assembly weighs as much as a h165 steel carrier.

My Gregories manual shows that the 1000 uses shims to control pinion bearing preload, while the 1200 uses a compression sleve & a good look at the pictures clearly shows that the pinion 'shafts' are diferent, so you would need to use the shim method if you use the 1000 pinion.

Will the two pinions interchange into the others housing? You would need to dismantle them & start measuring to know for sure, but Lagwagon is confidant that it will.

As for the case- diferential [hemisphere], here is what my books say

38241 - 18001 case- differential gear [1000] ALL - [except ute]
38421 - G0500 [1000] ute
38421 - G0500 [1200] ALL [except ute] In case anyone missed it, these last two part numbers are the same.

This means that the 1200 hemisphere should be interchangeable between the two diff housings as there was only one alloy diff housing part number for ALL B10 & B20 models. [38310 - 18000]
I hope that this helps.

I'm on my third alloy housing cause they tend to stretch when you put alittle HP thru them
Then they whine like a pig when the RPM gets up there in 5th
We hope to get a year out of this one before we change the whole car setup.

Thanks all, I will drop them both into Stewart Wilkins with the LSD and see if he can make it work.