will a vs series one motor fit in a vt series on without modifying the wiring harness
Yes....except I think you will have to change the thermostat housing as the VS has the coolant temp sensor in it and the VT doesn't. The VT injectors have a higher working pressure too, so you may want to swap them over.
what about the egr valve does that just bolt on to the new block and will it have the same power output
easiest way is to just use the intake manifold off the VS on the new motor (rather than using the VT one and sealing it off), but you'll need to replace the gasket and O-rings (about $70). for the thermostat, drill and tapper a hole in the front of the inlet housing to stick the temp sender (for the gauge) in which is on the VS but not on the VT
When i did mine, i used a VX motor. I just bolted the entire inlet manifold off the VS block onto it, and same with the vs exhaust manifolds. There was some pullies i changed as well because they were a different size for the belt i had.