Ideally the injectors and pump need to be serviced every 100,000miles or so when they are stipped down, worn components replaced and then re-calibrabrated, etc. Prices vary a lot depending on where you go (£300 upwards), but I know a good firm in Swindon if interested, although for them it's best if you remove the pump and injectors yourself.
Another more basic thing to consider is the fuelling. I can tweak the load volume screw on my 80 series and it can make a considerable difference to the performance of the engine - the more fuel you put in the more power you get out (obviously to a degree) - you need to strike a balance to get the fuelling right so that you get the power but aren't throwing out clouds of back smoke behind you. If you want to get technical about it also fit a pyrometer to measure the exhaust gas temperatures to make sure they stay within reasonable limits.
As for injector cleaners, there are a number of products on the market that can be added to your fuel, some are better than others, but generally only worth it if you know that the injectors are in good condition.
The best 'cleaner' I have found is 100% biodiesel, run a couple of tanks through your car and it can make quite a difference, although I don't know if the older fuel lines on a 60 will be able to tolerate it.
One final thing is that the fuel pump on the Landcruisers suck the fuel up from the tank and that side of things can get worn - to combat that you can fi a 3rd party pump (Warlboro is recommended) which will pump the fuel to the injector pump providing a consistant flow rate that helps the injection pump provide consistant injection pressures.
- Specialising in Land Cruiser preparation and servicing.