Installing an engine and transmission in a scratch-built vehicle is, in some cases, not as complicated as it may seem. As long as you have the parts and tools required - welder, level, tape measure, straightedge, basic mechanic's tools, and some patience - the installation can be completed by an enthusiast with moderate mechanical skills.
In basic terms, it's just a matter of bolting the engine to the transmission and then hoisting them into the engine compartment. Unless you can lift 1,000 pounds, this step is obviously best achieved with an engine hoist. Once the engine and transmission are placed in the vehicle, positioning and measurements for the engine and transmission mounts, radiator, and other vital components can then be measured. The key point that cannot be stressed enough is to remember that when locating the engine and transmission it is critical to always keep in mind the fitment of all the other components. In fact, it is best to know the exact measurements of all components. It is a very good idea to create a thorough list of all the parts that help make the engine run and then double- and triple-check that list.
The '99 Dodge 5.9L Magnum...
The '99 Dodge 5.9L Magnum engine ready for fitment.
Other factors to consider are exhaust system routing, the steering system (including the gearbox, tie rods, and pitman arm), driveline routing, and centering the output from the transfer case to the front and rear axles. This is only a start. Then there are cooling system components, electrical components and wiring, and air cleaner location for proper hood clearance. Your installation list should be long and distinguished.
If the transfer case is located on the driver side, then the motor and transmission need to be located 1 inch off center to the passenger side for proper front driveline clearance. If the transfer case is located on the passenger side, then the motor and transmission need to be located 1 inch off center to the driver side for the driveline clearance.
After everything is measured and fitted in the proper locations, all that is left is welding the mounts to the frame.
 We used a universal motor...  We used a universal motor mount system from Advance Adapters to mount this motor-and-trans combo. It provides solid mounting with the universal adaptability required for locating engines and transmissions properly. |  We used a universal motor...  We used a universal motor mount system from Advance Adapters to mount this motor-and-trans combo. It provides solid mounting with the universal adaptability required for locating engines and transmissions properly. |  One of the first steps of...  One of the first steps of the installation was attaching the motor mount plate to the engine block. |
 For ease of installation,...  For ease of installation, we removed the front grille from the vehicle. |  As you can see here, it is...  As you can see here, it is much easier to hoist both the motor and transmission into the vehicle when it is built from scratch. |  And it is much easier to mate...  And it is much easier to mate the motor and transmission when they are out of the vehicle. |