Info on building an adapter to use rod linkage on a 520 or 555 transmission:
Using differential brackets from a 555 and a 525, you can make an adapter to install rod linkage on a 555/520 transmission.
Download the PDF template below, cut out the left and right templates and cut the 555/520 differential bracket along the lines of the templates. (PDF Posted further down in the this thread)
Lay the 525 diff bracket on the newly modified 555/520 bracket as it is in the photos. Align the bottom hole of the 525 bracket with the bottom hole of the modified 555/520 bracket.
Tack weld the left side of the two brackets together temporarily. Bolt the assembly to the 555/520 transmission using the top bolt. Align the bottom hole to the transmission with a punch for now.
Adjust the right side of the 525 bracket until the pivot shaft is plumb. Clamp the two together and tack weld the two bracket on the right side.
Install the rear pivot bracket on your newly mocked up adapter. INstall the 525 selector bracket to the gear selector and install the linkage crossover rod between the selector and the pivot brackets. You should be able to shift the selector by hand into three positions. Adjust as needed.
Separate the two brackets and use a hole saw to cut a larger lower hole in the 525 bracket. MAke the hole large enough to pass the mounting bolt through.
Reassemble the two brackets aligning your tac welds. Weld the two brackets together for good.
There’s a knob on the bottom of most 555/520 diff covers, grind this off for clearance for your new bracket.
If you can build the rear bracket, the upper pivot is cake.
Cut and drill a piece of angle steel so it can be bolted under the top two diff cover bolts.
Get out your upper selector pivot bracket and lay it on top of your new bracket. Mark where the pivot shaft will need to be installed. Usually it lands just over the left bolt. Weld on the pivot shaft. (You need to make one)
Bend the selector pivot lever so it engages the black plastic selector knob.