You don't need much torque on the rear cam bolt to make it hold. The Volvo book spec is much higher than necessary. Clean all the oil and crud off the mating surfaces (back of the cam and front surface of the rear cam sprocket) to ensure a good, flat, tight, dry fit, then *lightly* oil the threads of the rear cam bolt and between its head and the washer. Then torque it to 30-40 ft-lbs. Will be more than enough to hold it in place, and will make it easy to get it loose again next time. The rear cam sprocket is not the crucial one, since if it does come loose there will be no lasting damage, the engine will just quit running until it is re-set. That's why it is just a flat fit, whereas the critical front sprocket is a taper fit and requires much more care. If that one comes loose, it means the end of the engine's life.
Timing it by moving the rear cam sprocket on the cam is the way to go -- avoids disturbing the position of the hard fuel delivery lines, and it is also much easier, faster, and more accurate than trying to move the whole pump.
HOWEVER: DO NOT BREAK THE BOLT LOOSE WITHOUT HAVING A WAY TO COUNTER-HOLD THE SPROCKET. If you try to break the rear bolt loose (or re-tighten it) with the cam only being held in position by the front timing belt, you will damage the front belt, and if that belt breaks, the engine is done. Many thousands $$$$ to fix it, if a fix is even possible, after a broken belt. YOU NEED MORE THAN JUST A WRENCH TO REMOVE THE REAR BOLT. You have to have a substantial tool designed expressly for the purpose of counterholding the sprocket and absorbing the torque, as well. Otherwise you can cause instantaneous engine destruction when you go to start it back up.
Sorry to word this so strongly, but unfortunately with a high-performance diesel engine like the D24, there is so little margin for error that you really can't afford to make even a little mistake when it comes to belts and engine timing. They are very unforgiving of errors and inexperience, and if you blow it up, finding parts to fix it will be difficult and very expensive. It's easy to do the job right, but you have to be prepared, and have the right tools and knowledge.
Might also want to have a look at your front belt and see if it looks like it's in OK shape.
It sounds like your car runs fine, so I would just not mess with it unless you have reason to suspect that the timing is not set right (smoke, hard starting, etc?). If you want to get the right tools and check it to see where it is, that would not be a bad idea, but don't try to start playing around with calibrations if you don't have the tools and haven't done your homework to make sure you know what you are doing. With a non-turbocharged engine, monkeying with timing and fueling will only gain you 2 or 3 HP, no more..... and if you don't know what you are doing it's more likely you will make the engine run worse, or potentially even do long-term damage to it.
That's a good-looking car. Don't see too many that color.
