No one can tell you which engine to use. That is a personal choice that is determined by many factors. The money you will spend, the machanical ability that you have, and what you will use the vehicle for, are some of the things to consider.
Double transmission are a definate NO. There are too many more practical options to get the gear ratio that you desire. Granted it has been done in the past. It was more work and trouble than it was worth.
To answer doctorj928's question: Putting one trans behind the other was to obtain the best ratio for a quarter mile drag strip, or circle track, as most people could not afford quick change rearends. Rarely did it work. To me it was not wort the trouble to have a worthless conversation piece. Mostly they were for getting an arguement started.
With the front box and back box in third gear you had direct drive to the rearend. With the front box in second gear the rear would give two lower than normal final drive ratios. The same with the front box in low gear.
Most of us ran a rearend gear that coinsided with second gear in the trans and RPMs that we could turn