The later 1990s engines will bolt into place. The problem is not being able to install and use the 1995 CPI Intake Manifold and fuel injection on the later 1996+ heads (which were changed for the new SCPI fuel injection). At least that is how I understand it.

Display photos (click on "info") for the AC/Delco intake manifold gaskets on Rock Auto for 1995 vs 1996 and you will see why.

I believe you can use the short block for later engines in a 1995, with the 1995 heads as long as it isn't a metric block (casting number ****090M). Metric block is tapped for metric starter and bellhousing bolts which can cause some starter issues even if you use metric starter and bellhousing bolts.