I just did that quest - taking E-class asteroid to Kerbin's orbit. That's pretty straight. Using procedural parts and tweakscale (for reaction wheels) I've created one of the biggest craft I've ever done - 700t tug, using only huge 3.75 reaction wheels and a bunch of vernor engines for rotation. Met The Rock in solar orbit, precisely docked (many quickloads, really) and took it to Kerbin, using MechJeb. Approximatly 10 years, btw... This monster also could be done only using stock parts - tug's tanks diameter is 3.75.