you would be completely insane to go through a dealership to buy a SBC
Agreed. Buy it from JEGS. Same engine, cheaper, and free shipping.
I have been all over 350 cam choices over the past several years. Do NOT buy the 350/290hp engine. The problem with the GM 350/290 crate engine (GM #12499529) is that it does not have the low end torque you need.
GM put the cam from a high-compression 1967 Corvette 350/350hp engine in a low-compression 350, and it has low static compression and a lot of overlap. What this gets you is horsepower up top, but no bottom end. At all. BTDT. With this engine my truck was a slug off the line, though it was a two-lane terror for passing. 50-90 mph times were excellent. 0-50 times were l-o-n-g. Particularly in a truck, this is a bad choice. This is also an old-tech cam grind with long ramps. Modern computer-modeled cams deliver much better performance for the same givens by speeding up the ramps. This gives longer closure times -- more dynamic compression and a longer power stroke -- with improved flow.
The better choice is to get the base GM 350/260 crate engine (GM #10067353), save yourself about $500 compared to the 350/290, and then swap the Comp Cams 12-235-2 cam into that engine before you even put it in. I swapped out the cam in my 350/290 once it had been in the truck a year, and it's a LOT more work to swap a cam after the engine is in the truck! This cam is a modern grind, will give you 300 hp, but will also give you almost 400 lbft of torque, with almost 300 lbft at 1000 rpm. Which means it will have grunt from the get-go, for getting off the line. Get too pedal-crazy with those numbers and you will get to know the people at your local tire store really, really well.
If you swap the cam into the new engine, you'll void the warranty, but them's the breaks. You also don't need to change out the lifters (which set up to the cam within the first hour of operation -- once the engine is run AT ALL, if you change the cam, you MUST change the lifters) or the springs (as the stock springs in the 350/260 engine will work fine with the 12-235-2 cam).
Now engine alone isn't enough. You also need all the right plumbing to get those numbers. I would recommend an Edelbrock Performer intake manifold, a Quadrajet tuned to order by Sean Murphy Induction, Hooker headers, and dual 2.25" exhaust through a pair of Flowmaster 40 (louder) or 50 (quieter) mufflers, with a 2" H-pipe.
That's about the cheapest high-performance new engine you can get. If you want to go crazy, get the 350/260hp crate engine, put the 12-238-2 cam and a set of DART heads on it, and you will have 400hp and 420lbft of torque. That would be insane, but I know someone who did it, and he loves it.