Always a topic bound to start arguments, and I would be extremely interested in hearing from others who have either conversion and what they think, especially someone who has had both.
First off, I have a chain/cross-over type of conversion and have had no issues or problems or anything with it. The one downside is probably that the heater doesn't seem to work overly effectively. Whether that is just the way '84 heaters were or it is effected by the conversion, I'm not sure. I probably guess it's the latter. However, it is a sunny Sunday afternoon car so the heater doesn't get used a lot. Neither does the A/C for that matter.
Technically, I see nothing wrong with the cross-over conversion theory if it is done well. Done badly may be a different story. It leaves everything where GM intended. Steering and suspension geometry are not effected, the firewall is not cut and shut and the engine is not offset from it's original location. If it wasn't safe, then surely it would not be legal. Having said that though, I don't believe that it is legal in every state, but I may be wrong. My car, though, is an auto, so it doesn't have the constant pivoting forces on the clutch pedal to worry about. God knows where you put a clutch pedal in the right hand foot-well of a C4 anyway.
Others will argue that the complete mirror is the only way to go. But having played around in a C4 engine bay I can only imagine what sort of nightmare that is. And a C5 must be worse.
I would love to hear some input from someone with automotive engineering knowledge, who knows Corvettes and DOES NOT have a vested interest in a conversion shop.