I'd say the best bang for your $3000 is a 400 shortblock, with your heads. A 350 can be built to make power. But it's just easier and cheaper to do it with more cubes.

Here's one for $2400 + shipping. Get him to build it with 5140 RPM forged rods, add a decent cam and your heads, and see if that's enuff spunk for you.

http://lenwilliamsautomachine.com/400_Short_Block.html

Or, for around $4000, you can buy a complete 400 longblock.

http://lenwilliamsautomachine.com/400_Long_Block.html

Want more ? How about a 400 block 4.25" stroker shortblock and your heads.

http://lenwilliamsautomachine.com/455_Short_Block.html