The case is done professionally. I don't even bother trying to do cases myself anymore -- its not worth the time or effort, what with messy stripping, then etching, then several spray coats. I drop them off at the powdercoaters -- the cases get acid stripped, washed in iron phosphate, then coated. You get a beautiful even finish with a surface that is supposedly harder and more rust resistant than the original.
Get rid of the 2SC1451's on the buffer amp. Replace with a decent TO-126 tranny (getting tough to find, but Mouser has some new 2SC3902T devices on order from On-Semi...these and the 2SA1507T should be used to replace any 2SA809/810 and 2SC1451/1452 devices you find in any gear you service).
The relay that worked as a drop-in replacement has been discontinued, unfortunately. There were also two styles of output boards, one where the relay shorts the signal to ground (rare), and one where the relay connects the output to the RCA jacks (common). In any event, I've not yet researched a replacement.
I usually shoot the trimpots on the PS board with Faderlube, and if they appear to do the job OK, I let 'em stay.
That relay you've linked to is the correct one for the main relay but there's another one on the underside that we were talking about that is unobtainable.
The soft-start relay is fairly easy to source...your link is correct. But the output relay is a small reed-relay soldered to the PC board. US Relays had a replacement for a while that was a drop-in for the non-shorting style of output board, but it is discontinued. But, there's always a way to make something work, if need be.
For the 'shorting' style of output board, I never found a drop-in. Had to get creative.