Personally, I would drive and enjoy it the way it is.
If I just had to do an engine swap, I would put a 360 in it. (best option for a well balanced, fast, street car)
If I just had to have a big block (but this isn't something I would even think about doing), I would do all the other (in my opinion "Needed") upgrades first.
Like:
Disc Brakes and Suspension for starters.
In todays world of stroker small blocks, I just don't see the point of a big block swap with it's added complexity and weight.