The last two are similar to(if not exactly) the ones that were sold as BTO options on G4s.
I have used these pretty extensively. I've used both the Apple OEM Adaptec 2930 and a generic 2930 that I found in a box at surplus. I've used these both for internal and external devices. Remember that a SCSI bus needs to be terminated at both ends, and as far as I know, they are self-terminating. This means that if you are using only the internal or external bus the card takes care of termination, although if you have things connected both internally and externally you will need to be sure you terminate at both ends.
The connector on those is a 50-pin high density Centronics, which in my experience is a bit hard to find. I have a fairly long one that has that connector on one end and the standard 50-pin Centronics on the other end. The standard 50 pin Centronics looks like an old parallel port printer cable, but is a lot larger. Most external SCSI devices have at least one of this type connector on them.
I also have an Adaptec 2902 that I ran my scanner on for a while. This has(only) an external DB-25 connector on the back. Some SCSI scanners I've seen(including my own Sprintscan 35+) have a DB-25 on the back, which just means that can just use a straight DB-25 to DB-25 connector. Otherwise, you'll probably need a DB-25 to 50 pin Centronics, which is equally easy to find. Depending on what type of connectors are on your scanners, you might need either a second DB-25 to 50 pin Centronics connector to connect them, or a 50-pin to 50-pin cable EIther is easy to find.
In any case, stick to Adaptec cards and you likely won't have trouble. My experience is that many Adaptec cards are plug and play under Tiger, but forget getting them to work under Leopard. You may need to dig around on Adaptec's website to find OS 9 drivers.
Also, since you're using multiple devices, you need to be very careful with setting IDs and termination. The IDs really don't matter(although avoid 7, as it's often the ID used for the card itself) just as long as you don't have two devices with the same ID on the bus. Most scanners that I've seen have some sort of dial or other similar adjustment on the back that makes setting IDs very easy. Many scanners also have internal terminators activated by a switch-be sure the first scanner is set to "off" and the second is set to "on." If the device doesn't have an internal terminator, you will need to use an external terminator, which will plug into the other SCSI port on the device. Most that I've seen for this sort of application are a small plastic box with a 50-pin Centronics connector, although you can find them in pretty much any configuration you need.
A couple of other things from your first link-several of those appear to be the "Jackhammer" ultrawide card that was sold in some Powermac G3s and G4s. This was intended for driving internal 68 pin SCSI drives on these computers. Apple was pretty explicit about not using external devices on these drives, although they would probably be okay since you wouldn't be using internal devices. None the less, the external connector is-I think-a 68 pin high density Centronics, which is more difficult to find than the 50-pin version. This card is the Adaptec 2940.
I'd also recommend avoiding the Adapted 39160. I have one-it's a great, high end 64 bit card with two separate SCSI buses(both with internal and external connections) but in my experience it can be a bit cantankerous. I have it working now to drive a pair of 10K 68 pin UW drives in my Sawtooth. I don't recall what exactly I had to do to get it working, but it took a fair bit of tinkering.
If you are going to buy an Apple OEM card, stick to a 2930.
