Yes, it can be installed backwards.
Anyplace that sells Volvo parts should have the seal ring.
I have updated timing covers for the B30 seal.
email me offlist if interested gdowns [at] cableone [dot] net

Not really. One side has to run against the end thrust bearing. When installing, I think the cam's keyway is straight up at TDC 1 & 4.

If it has no dots, all you have to worry about is that 1 or 4 has it's valves giving close to equal lift when the pistons for 1 & 4 are at TDC. One tooth either way & that won't happen.

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Three 164's, Two 144's, One 142 & a partridge in a pear tree.

Is it a fiber gear or steel? Usually the fiber gear has a radial groove (cut) at the line up point. A rough positioning (just to find the mark)is with the cuts for the keyways to be both upwards. Check both sides of course and the back of the gear would have enough room to clear the bolt heads of the thrust flange. Hope this helps.