For a car of that vintage and size/weight, if you are wanting some GO along with some MiLEAGE which added together equals SMILAGE-----I would suggest an upgrade to a later EFI takeout of at least the mid 90s to present------if you do a 90s type LT or vortec all your exhaust and mounts plus trans will work but a later LS will need different mounts/exhaust, possibly will want to do an electronic control OD trans-------I would not recommend a crate engine as an answer to your stated get up go moleage---and if you do upgrade you can probably sell off the 283/327 stuff to collectors-----------