That is the correct relay, except you will have to clip off two of the pins. They are not used anyway and the board has no hole for them. It will give you two paths for the signal for each channel. The original only has one path for each channel. It gives better reliability because if one path fails from carbon scoring the other will still work and you will not know the difference.
Those are the diodes I use to replace the 1S2473D as well as the 1S2471 in other amps. For the 10d2 diodes, I use 1n5393S to replace them. For the RD-13E zener diodes I use BZX79C13. You should replace the RD-13E while you are in there. Zener diodes are not known for their reliability over the years.
All fusible resistors should be replaced. It's best to use flameproof. They have a coating that will not allow them to burn should there be a short and they get hot. The fusible resistors were supposed to blow first and prevent further damage. As it turned out they blew after the damage was done. So they served no purpose and will rise in resistance over the years until they finally go open. Sansui seems to have switched to a different kind in the last units made that is not as bad as the first ones. Still I replace them. Replace R23 and R25 on F-2721 and F-2722. They are 150 ohm. Replace R47, 48, 49, and 50 on the F-2723 board. They are 82 ohm. Replace R37, 38, 39, and 40 on the F-2720 board. They are also 82 ohm.
Yes, replace the 2SA726 transistors with KSA992FBU. The pinouts for the two are opposite, so put the KSA992FBU in backwards in relation to how the original transistors are installed.
The relay is run by TR603 on the F-2663 board. It is a 2SC945. It is still available from MCM electronics I believe. Or can be replaced with a 2SC15090S-ND. The pinouts are the same so the orientation is the same. A direct swap. You could also use a BC237B, but the legs would have to be overlapped because of the way the pinout is.
I usually replace D608 because it is the protection diode for the reverse currant from the collapsing relay coil field. I use a 1N4004 for that. Easily found and fairly robust diode.
The trimmers are 100 ohm, 1K ohm and 2.2K ohm. I use the 3386 model. Either F or G whichever is side adjust I don't remember right off hand. The other style is top adjust.
I don't have a means of posting pictures right now. But just lay two diodes side by side. One with the band away from you, one with the band towards you. Bend the two leads that are away from you toward each other and solder them together. Cut off the excess length down to the solder. Now cut the lead near you on the banded end short so you will know which is the negative lead and cover the thing with heat shrink. Remove the VD-1212 from the board and install your replacement with the short lead, that you cut, at the hole the arrow points at.
Hope this clarifies it all for you. If you need more help just ask.