Brian Ristuccia wrote:

I have a 3 disk raid5 array which recently suffered catastrophic failure of
one disk. While the array was degraded, one more disk failed out of the
array due to a bad block. Investigation with badblocks reveals the marginal
disk has only a handful of bad blocks.

What I'd like to do is start the array with the good disk and the marginal
disk, add a 3rd known good disk, and rebuild the array as best as possible.
Then I'd fail the marginal disk and install another good disk.

Well, first of all - don't do anything without verifying it first.

There's a good chance you can recover quite some data if you don't screw 
it up by 'having a go' (I speak from experience :) )

Instead of your plan, can I suggest you try to duplicate the 
disk/partition showing a few bad blocks onto a known good disk.
Then forcefully reassemble the array, then add another good disk for 
reconstruction.

Useful tools include dd_rhelp and dd_rescue

Take a look in the archives as this kinda hit me recently.
http://marc.theaimsgroup.com/?l=linux-raid&m=110025421113782&w=2

David