The ANSWER to the OP's question is NO. You cannot bore a 273 to 318 bore size. There is too much difference between the 3.625 and the 3.91. That's taking 0.142 out of each side and most Mopar blocks have minimum wall thicknesses of around 0.140, some have even hit the streets with spots thinner than 0.090. As the minimum non-thrust thickness for an acceptable hot street build is 0.100", you can see why it wouldn't work.
Now on to stroke. I am sure you could put a 3.58" crank in a 273 block, if the crank had the right main size. At stock bore it'd be a 296. It'd run noticeably stronger than a 273 but would have peak hp earlier.
I hear the people screaming "a 318 is still bigger and you can get them for free!" That's true and this is a discussion of THEORY, not in the real world where one has to pay for things.
I'm not sure if a 4.00 crank would work in the 273 block because the bores are so small that the connecting rod could run into the lower edge of the bore somewhere mid-stroke. It'd have to be checked out. A stock bore 3 5/8 x 4 motor would be a 330. It'd have really good low-end torque but would run out of breath early because the small bore limits breathing.
ANY of these theoretical engines would require custom pistons, which would be extremely costly, except for the fact that any high performance 273 piston is also going to be a custom forging. So in reality, in our theoretical world, that part of stroker-vs-non stroker cost washes out.
If anyone was REALLY interested in doing something like this, and again why would you want to, the Toyota 22R motor has the right-sized piston and its 0.866 pin is also one of the NASCAR pin sizes, so it may be possible to use NASCAR rods in this engine.
Those of you who are tempted to pile on with the "take-your-pick engine would be cheaper and more powerful" post, just put a sock in it. Those comments have already been made and aren't the answer to the question in the original post.
I love these paper engine builds, once in a while something real pops up from the study.
R.
