to answer your questions...
stroke kit:
by using a different crank, rods and sometimes pistons, more displaement is acheived. in most cases, the crank has a longer stroke. the rod length is shorter, and the piston will sometimes have a different mout location onto the rod to try to keep the oem geometry. problem is, none really even comes close. if you stroke the motor, your rev-happiness will go bye bye. it will still go to 8k, but the top end won't be as "b16-ish" as it is now.
i highly recommend doing something else instead.
this will cost you 3k for most kits out there.
sleeving the b16 to 84mm over the 81 will put you at 1.7 and change, still keep the stock geometry and make more power. but, this is also costyl- 1000 for sleeves, 500 for 84mm pistons, and you might as well do rods for 350-500 while you're down there along with new bearings ~100.
going to an ls block or a gsr/itr block is a better idea, and the cheapest by far. like pills said, it cane be done for under 500 bucks, or a little more if you start hitting aftermarket parts.
but then, you can always sleeve or stroke this larger block too if you wish down the road.
going to a better base is the way to go IMO