I just did this job (except for the water pump) on my "new" '93 940. Comments:

I had the radiator out for a repair so I left it out for the other work. I'd definitely loosen the fan and set it up on the side of the engine.

I used the Volvo counter hold tool to lock down the crankshaft. Well worth the money. I've done several Volvo t-belts with it.

I held the cam and aux shaft sprockets with a rubber strap wrench. Easy to use, no damage to sprockets.

For timing marks on the crankshaft, I used the marks on the seal carrier in back of the crank sprocket at about 11:00 oclock. You can't use the 0 degree mark on the front cover because the cover will be off the engine for this step.

The crankshaft sprocket setup has a notch in the front, concave guide washer. Line the crankshaft up so this notch is in line with that mark on the seal carrier. The camshaft and aux sprockets line up with small dimples and bumps on the rear t-belt cover which you've replaced after doing the seals. Actually, if you have the engine with the distributor driven off the back of the camshaft, the position of the aux shaft isn't important for timing.

I replaced the crankshaft and aux shaft seals by removing the seal carrier and R&R'd the seals on the bench. A good thing too because the seals were so baked into the carrier that I had the take a hardwood dowel and hammer the old seals out. I probably would have scratched up a shaft if I had tried to remove them in place. I was able to reuse the paper gasket between the seal carrier and the block. A good thing because the local Volvo parts guys could hardly figure out what gasket I wanted and would order one with at least a week's wait.

I replaced the camshaft seal by removing the camshaft cover and the front cam bearing top half. The seal comes off with finger pressure this way and the new one slides on easy (don't forget to oil the seals!). I reused the cam cover gasket but should probably have used a new one.

Hope this helps. This is a satisfying DIY job for sure.