Hey Wayne, ypou can email me if you need me to help you shop with some advice.....
96 vehicles have OBDII and pre 96 have OBDI. THere's benefits and drawbacks for each, but all in all not a big deal. Just be sure to get the LT1 (duals). Most important.
Next try to get the G80 rear end (posi). This will be listed on the SPID label on the underside of the trunk lid, along with all the other "RPO" codes.
Try to get a 9C1 caprice (listed on label), it will have a heavy duty frame, heavy duty oil/trans/pow steer coolers, guaranteed.
Also look for rear disc brakes, some caprices still use drums, some don't.
Look for a good rear end gear ratio, most will have a 3.08 rear if a 9C1, but possible 2.93. I am not too sure, but some may have had 3.23 or so, but I believe those were rare. 3.08 will probably be the best you get. Check the SPID label for these codes