Cummins swaps.....Who has done them? Need some advice

[Chevy3+3]

I have been through the build threads and no one seems to ever finish a project or are they are still in progress. I have some simple questions I hope some of you can answer. Someday I would love to do a Cummins swap but don't want to jump in not being prepared or educated.

My truck: 88' Chevy V30 4x4 CC Dually

Current drivetrain: 454, TH400, NP205

My questions:

1. What is the difference in the 1st & 2nd Gen 12 valve Cummins engines?

2. Which would be a better choice?

3. Which manual transmission would be the easiest to swap in. I would love a Manual tranny but would think a little more work would be required (clutch pedal, clutch master cylinder, etc.).

4. If I were to use an auto tranny what would be my best option with simplicity and dependability in mind.

5. Are body lifts usually required for firewall or tranny clearance (depending on tranny)?

6. Can I utilize my factory radiator support and radiator? Or are mods definatley necessary in this area?

7. Are there any prefab or factory built mounts or crossmembers for these types of conversions?

Thanks to any and info. I just hate going into a project like this halfa## because corners usually tend to get cut at that point. If I decide to tackle this project I want it to fit well and be dependable.