A 351w fits nicely in a 65/66 engine bay. As mentioned, the main (and most expensive) problems are headers and getting adequate cooling. Many items from a 289 will work on the 351w. Transmission, bellhousing, flywheel/flexplate, timing cover, water pump, balancer, pulleys, and motor mounts can all be used (assuming that the belhousing is a later 65' or newer 6 bolt unit.)
Some things are different, such as the brackets for the alternator, and AC unit. Very few of the actual engine parts are interchangeable, except for items such as cams, lifters, and heads.
I bought custom headers to make the swap. Actually tins is the second 351w swap I have done. Nearly all headers will have some interference with the shock towers due to the close quarters so don't expect them to slide right in with out a little modification to the tubes or the towers.
As far as cooling goes, I first used a 20" radiator from a 67' AC stang. It was barely adequate and would overheat in summer. To solve the problem, I upgraded to a 24" radiator which works very well. Aluminum alternatives also might do you well.
Unless you are planning on adding a hood scoop, you are limited to running a low rise manifold like an RPM or Stealth. A Vic Jr. is out of the question as it sits too high in the engine compartment. Spark plug changes are really fairly easy compared to many factory mass produced V8 vehicles in the 70's and 80's.
As far a how it runs, well, you really can't beat the torque from the larger engine. My stroked 393 will light the tires when I punch when rolling at 40 in 3rd gear. Probably more power than what is needed in a daily driver, but it sure is fun. I have no strip time, but hope to get it on the dyno soon.