Despite protests from others this works. This is on B21/23 8 valve engines, 84 and earlier for sure. This may not work on the B230.
Remove alt., PS AC belts
Remove timing belt cover
Loosen tension on old belt, slide it off cam pulley and intermediate and idler, then wiggle it off crank pulley, it can be fished out between the U shape lower metal guard and the crank pulley.
The new belt goes in the same way, lower it below and behind the crank pulley, push it on edge through the gap between the crank end and the metal guard, then wiggle it back onto the crank gear.
I have done this about 4 times on 81 and 84 240 volvos.
Admittedly it's impossble to see the lower timing marks this way, but I haven't missed yet using the marks on the pulley and block used for ignition timing.