what is the best small block and why ?

I think that site is pretty good since they have everything in a kit ready to go. I do not know another place off hand that you could compare prices to, except maybe Manciniracing.com. (Maybe)

The problem with factory heads is they will not support the engine size as cast. They will need to be ported and milled for for this C.I.D. Factor X,J etc... 340/360 heads are approx. 72cc's which would mean some milling would probably be required. Watch the head gasket used for this. Not to thick!

Depending on cam size and actual compression ratio, then and only then can a HP/TQ figure be given.

What operating RPM do you want to drive on the Hwy. in? What gear ratio\tire size?

I can plug it into a desk top dyno sim. The program is a little old, but in general, it isn't bad. A little generous in the HP category.