273, or 318?

After reading all this I was thinking why not just find a junkyard 5.9 and o.d. trans. all together. Couldn't be that much cash and you would have the bigger, torquier motor gets decent fuel economy and still run a 3.73 or 4.10, best of all worlds. So guys what would a junkyard 5.9 and trans cost? My guess $700.00? Cheap deal.