As the title states, I just did this as my HX35 crapped out, and I sourced a good used one from an 01. The following had to be done to make it work:
1. Swap exhaust elbows, mine was a 2 piece with a circular clamp. The 24v elbow only uses the 2 bolts that are a pain to get to.
2. Change out oil supply fitting: the hoses aren't the same, but the threads where the fitting mates to the turbo are.
3. Drill out the upper 2 mounting holes. My 12v turbo mounted w 4 studs, the 24v turbo hade 2 studs in the turbo, and 2 in the manifold.
4. grind the waste gate bracket to clear one of the hard coolant lines.
5. reroute the small line from the waste gate. On the 24v it goes to a fitting on the bottom of the compressor housing, this needs to be plugged. Reroute it to meet the original hard line.

No gains to be had, other than a wider range of years to source a used turbo from, thought I'd pass it along.

 

A few years back I installed a 2001 HX-35 on my 95...It was not that hard of a swap...as you mention a few modifications...

 

I would say it would be easier to just remove the hard line, since the wastegate position is different from the early HX35's to the later ones.

 

just posting this in case anyone else ends up searching in the future. A few pics to show what is different.

 

I'm picking up an HX35 from a '96 12V that I'm going to run in my 24V. I thought it was a direct swap but sounds a little more than what I was expecting.

 

Try an he351ve lol it takes more time. Good info to have thanks edse!

 

Not interested in the HE351 but thx

 

im still working on it....it has an exhaust brake feature in it thats why im putting it on. building controls at the moment