Installing them yourself and aligning the engine is not difficult, but it takes time and you must be a perfectionist. Use hydraulic jack (or two) under the oil pan with a large block(s) to spread the load evenly .
All four engine mounts must have equal load will no side stress.
I found that the easiest method was to do a course engine alignment with the mounts attached to the engine, but not to the stringer or mounting rail. With the mounts sitting flat make the height adjustment with the bottom nuts and slide the engine side to side if required for lateral adjustments.
Then drill the engine mount holes in the stringer if necessary and tighten it up.
Then check the alignment again, and make any fine adjustments required.
The final adjustment and alignment check must be done in the water as the boat will flex differently in water compared to on the hard.