I'm right in the middle of building a 1971 GMC Pick up. I'm stuck on motor options. Build one from the ground up at 8.5:1 and a blower or just buy a world motors 454 small block. If anybody has some tips to make my choice easier would be thanks. This truck has been back-halfed and tubbed with the new MT Sportsman 31" tires on it and lowered 2" front and 4" rear. It is a auto with a custom moser 12 bolt rearend in it with 4:10 posi in it. Street cruzin with the head snapping power is what I'm going for. I live 500kms from the nearest track so racing is out of the question but for the open track day. Thanks to all those who give there advise!  

You would be much better off with the small block, not to mention the huge weight savings, blowers cause some problems.
No vaccum for power brakes and timing advance.
Blowers push alot of heat into the oil and cooling systems.
Hood clearance issues.
Asscerory drive options are expensive.
Special care must be taken when you build up the engine to make sure the lower end will handle the boost and added torque.
The fuel systems are total differant.
You will have to run a boost control on the ingiton.
And on and on.............
If you like to ride in your truck more tha work on your truck, buy the world small block.  I have a world 427 and it has been flawless.  

If you go with a centrifugal blower, hood clearance isn't an issue. Add an intercooler, and heat isn't an issue with any blower.

On accessories, most blower kits are designed so you can keep the stock accessory drives. That won't be a problem.

As for the blower killing vacuum, that's not really true. I've seen blowers installed on several late model cars, the stock brakes and vacuum booster work with no problems.

Boost control on the ignition? Also a new one. You can if you want, but if you set everything up correctly it's not necessary. You'll definitely want to go with an aftermarket ignition like an MSD unit so you have plenty of spark energy under full boost.

Building the motor, you want forged pistons to give you soem extra protection against detonation. Other wise, you'd build a strong bottom end no matter what (forged crank, good rods, rod bolts, beefed up mains), so you'd be good there.

Fuel systems aren't totally different either. You will have to install a higher pressure/volume fuel pump so under full boost the motor doesn't starve for fuel and go into a super lean situation. This part all depends on if you plan to run a carb of FI.

If you want to build up a small block with a blower, call a couple of the blower companies (ProCharger, Vortech, Eaton, Weiand, etc.) tell them what you'd like to do, and ask for their advice, and what kits they have to fit what you're building.