[PxTx]

I've got the most experience wiht MSD, but my expectations would be the same for all CD ignition boxes.

The first noticeable improvment is usually just what you want. Smoother and stable idle. The CD systems lower COV (coefficient of varioation)and as an additional benefit plugs don't foul as quickly.

Improved HP may only be a few on the top end, but I bet the whole curve is up a few hp in reality. I also think in the upper R's the CD does a better job of lighting all of the fuel. Just bolting an MSD on without an ignition re-tune may also lead to underwelming results.

I think you are right that the old MSD box could probably take the new parts, but they don't want to invest the labor. You are more motivated to make it work. MSD now has the stuff already potred in the boxes and coming from China. If they were still making them the old way, they could re-use your housing no-problem. I look forward to seeing your results!