A lot of people put 253 Holden motors in them. The old 4 speed box cant handle the torque though and normally strips 3rd gear. It is also a bit of a tight fit so you have trouble fitting a decent sized radiator in. There isnt enough room to fit the fan in front of the water pump so most people run thermo fans which are ok on the road but are not up to the task when you are going slow in hard going off road.
The old 18R can be sorted out so they go ok. When i had a Hilux with an 18R in it i put a DGAV weber carby on it and it made a big improvement. I ported the top of the inlet manifold to match the base of the carby, put electronic ignition on it, a set of headers and 2 inch exhaust then did some work on the head. If you can find a head to suit a 74 corona, use it because they flow better than the later18R heads. The later heads have some bad casting marks in the ports that upset flow. They can be cleaned up with a die grinder but it is a fair bit of work.
A 22R should bolt up to your bellhousing but you have to get the right one to match the position of your engine mounts. Some 22R engines have a couple of positions for engine mounts.
If you want better brakes the discs and calipers from an LN106 Hilux bolt straight up. The discs are vented and the calipers have bigger pistons and pads so they have more clamping force. You need to either cut your backing plates or use the later hilux ones so the bigger calipers fit. FJ60 or HJ60 Landcruiser discs and calipers are the same as LN106 Hilux ones. Use an FJ60 Landcruiser master cylinder with the bigger brakes because it has a bigger bore, so it suits the bigger calipers. It will bolt straight up to your power booster but you will have to either make up a new brake pipe to go from the front of the master cylinder to the base of the power booster or bend your original hilux one. With the hilux master cylinder the front pipe comes out the top but the lancruiser master cylinder has the pipe comes out the left side.