Since you have 4k to play with, I am assuming you just want a high performance engine, not necisarily a high Cubic inch engine(383, 400 427 etc.), i would stick with the 350. . On crates they overcharge on labor and such. If you put that money into that motor, witht he right heads, cam, and labor, your 350 will out perform any crate you can buy for 4k. and you will still have some change left.
This is assuming that the 350 is still running and in usable shape.

as for the web site, www.summitracing.com
i shop here.