I am in the final stages (though some here might think that it will never be completed...[img]/wwwthreads_images/icons/smile.gif[/img]) of installing a 4.5" SPOA.
I think that the main advantage of getting a bolt-on SPOA (I think Rocky Road has the market cornered on them) is the fact that you can adjust the third member angle after they are installed. You may -- no make that will -- need to buy new U-bolts but you don't need to grind off the perch welds. So if you screw things up handling-wise (especially in the front), it is an "easy" fix that does not destroy your axle. And THAT is important!
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ack,,,I doused the ubolts in some ER (energy release) penetrating oil a good day before I tried to take them off.
.. and turned the axel over and took my wire round brush on my drill to the threads to clean them out.
then sprayed the oil on them again and they came right off
that way you don't have to cut the old u-bolts off...
<font color=red>Rich</font color=red><font color=green>_</font color=green><font color=blue>(</font color=blue>
If you do not expect the unexpected, you will not find it.