It really depends on what you want for a final product.

Downsides.
#1 your truck wont work for months
#2 it is going to be difficult to chase all the details out.
#3 it's gonna be expensive
#4 it's gonna take more time than you thought, and be more expensive than you thought.
#5 You're going to have to learn GM EFI and GM electrical systems..... may, or may not be a problem.
#6 It is going to be what you put into it. It will be as reliable as you engineer it to be.


Things I like about my truck.
#1 it hauls ass
#2 it will get 20 mpg when driven conservatively.
#3 it is easy to work on.
#4 is reliable
#5 parts are common, and cheap....
water pump 15.99
alternator 80 bucks
starter 50 bucks, and takes 5 mins to change.

#6 no timing belt to EVER wear out, and grenade my motor.
#7 No retard wiring stuff. (white with blue stripes, and red speckles with yellow bands)
<img src="/forums/images/graemlins/rolleyes.gif" alt="" /> <img src="/forums/images/graemlins/rolleyes.gif" alt="" /> <img src="/forums/images/graemlins/rolleyes.gif" alt="" /> <img src="/forums/images/graemlins/rolleyes.gif" alt="" /> <img src="/forums/images/graemlins/rolleyes.gif" alt="" />
#8 2.72:1 low range. While it's nothing to brag about, the fact that I got it as a bonus is awesome. (terra low kits are redaily available.
#9 my truck will run upside down, and I never have to look at a stupid carb ever again.

Those are the things I come up with off the top of my head.

Ive driven 2.6 raiders, and 3.0 raiders... Had a 2.6 turbo in my truck before I went 4.3. None of them drive as good as mine does now. <img src="/forums/images/graemlins/kewl.gif" alt="" /> <img src="/forums/images/graemlins/kewl.gif" alt="" />