Ive done both, I like out the top better.... I have done it in an hour....

This last time, I trimmed the cowl back to fit the intake, and I put the engine/6speed trans in together from the top in about 45 minutes, just have to put the headers on.

 

Out the bottom, ...

Easier for me, when I did a whole mess of things at once.

 

I did a engine swap a couple years ago in my 02 Z28. Replaced my blown LS1 with an LS6. It was much easier, for me at least, to remove the entire front Suspension, cradle, engine, wheels. I put the front wheels on after getting everything disconected, used a crane type machine to help lift the front end of the car off of the front suspension, engine, etc then rolled the entire assembly right of the lift and lowered the car. Did the same when I put the LS6 back in. Just used the crane to pick the LS1 off the cradle after unhooking everything, held the LS6 in place, hooked it all back up and rolled the assembly back under the car and lowered the car back down on top of the motor. I guess than, that I took the engine out from the bottom. Worked pretty damn good for me. I used a great guide. It was "How to Build High-Performance Chevy LS1/LS6 V-8s: Modifying and Tuning Gen III Engines for GM Cars & Pickups." by Will Handzel

 

Has anyone done this before or do you have to pull the trans before the motor?

 

Have to pull the tranny.