81 Rear axle swap 3.90 to 4.3

[dotts5]

my 81 fiat spider shredded some teeth on the diff and i was looking at replacements and had some swap questions on the 390 to 430 swap. i have seen posts in a forum about changes needed for the swap, but i just have a couple more questions about the change. I found just the diff for a 430 and wondered there is no way to bolt in the back half of a 430 diff with a 390 since they are different shape correct? it was described in that forum post that the back section of the drive shaft also must be replaced along with the Panhard rod. Since they are two different housings i assume i cant just slap in the 430 diff into my existing 390 housing by just removing the damaged 390 back end and draining and cleaning it out right? That seems like it would be just too easy! If i do go with the 430 swap i just need to track down the back section of the driveshaft off of a 430 set up car and a full axle and diff assembly from a 430 year spider correct? I apologize for all of the rhetorical questions, i have read a lot but just don't feel confident. Has anyone performed the swap recently that could give some pointers? Like will the drive shaft flange from my 81 spider bolt up to the 430 axles? will i need to get axle shafts to fit the 430 other than use my shafts from the 390? New to the forum and appreciate all the help i have had received from SocalMark, from reading all the posts with great answers, and to all who answer the post.

Cheers

[divace73]

I've actuallt got a 4.3 Argenta diff complete in mine. I had somebody weld on the brackets and panhard rod bolt and replaced the whole unit. I little heavier but Much much stronger and great for cruising on Highway
(I also have the 131 gearbox in mine as well)
Edit: Now thinking about this It might be a 3.4?????

[azruss]

dont know how much this applies to your situation. I just put in a 71 rear end on my 80. The panhard rods are different. the newer one has an offset it in to clear the larger 80 rear end. The drive lines are different length, but everything else matched up without any issues. I also traded out the springs as well. wanted to get that ass out of the air.

[dotts5]

Thanks for the answers guys!

Azruss: the drivlines being different lengths is what i was looking for. Thanks again!