v8 Astro

I was just wondering if the 88-94 Astro's came in v8?

Not from the factory they didn't. Many people have swapped a v8 into the astro though.
See www.astrosafari.com (http://www.astrosafari.com)
www.racecraftconversions.com (http://www.racecraftconversions.com)
www.jtr.com (http://www.jtr.com)

How big of a v8 can fit under a astro??

Read the websites I listed and you will find that any First Gen SBC will fit. BBCs can be made to fit. As will as the new LS1 motors. There's even a guy with an AWD LS1 at astrosafari.com.

stick with a regular oldschool SBC, and go with a 400SBC, a 383 stroker SBC or a 377 stroker SBC