No Limit or PorterBuilt or What?

[summitflier]

You'll probably get more opinions about engines and trans than suspensions

In any case... what are the plans for the truck? How do you want to drive it?
Sport Truck? Street/Strip racer? Towing anything? Daily driver?
Does gas mileage matter? How much? Do you want overdrive?

If towing and torque matter, get a big block.
If gas mileage is important you can always go with a 6cyl and/or an overdrive tranny.
My personal opinion (opinions may vary) is that for general all around driving, a good ole small-block is hard to beat. (I'm in the process of putting in a 383 stroker/700R4).
If you can afford it, a newer LS engine is a popular option. Better gas mileage and more power than the older style engines.