Howdy EB,
This is the other Schjeldahl brother. This is probably more than you wanted to know, but it should help.
Swapping in the 200 will virtually a bolt-in operation. The 250 may be more complicated, depending on the replacement engine.
Since you have a '67, you SHOULD have the 3.03 three speed std tranny. That will bolt to the 250 bell housing. BUT (don't you hate big BUTs) if the 250 doesn't have the std trans bellhousing AND flywheel - they are VERY hard to find. You CANNOT use the 200 bell, flywheel, or water pump on the 250. They have different bolt patterns.
The 250 is about 3/4 wider at the engine mounts, but you can just redrill the holes in the mounts to make them work. The 250 is about 1 inch taller. Can one inch be a problem? The 250 engine itself is NOT longer, BUT (another one) the water pump IS slightly longer - making the overall length about 1 1/2 inches more. There is NO substitute for cubic inches for pulling power. My brother has a 250 in his ranchero and I have a 200. His pulls because it has torque. Mine Pulls because it revs to six grand in a wink. Pick you poison - bith work.
The '72 200 is a SIGNIFICANT improvement over your 170. You get 7 main bearings, a much bigger intake log, provision for a larger carb, the ability to bolt in a DSII (your 170 work need LOTS of modification to do that).
The 200 is a direct swap. If you have not done engine swaps before, this is a GREAT learning step. You may have to use the 170 water pump, oil pan, and oil pump pickup tube. The 170 bell housing and flywheel will bolt right on to the 200 (use a torque wrench). Compare the exhaust manifolds. On non-EBs the 170 is MUCH smaller in volume and header pipe size. Use the '72 200 exhaust manifold even though you'll have to make a new exhaust pipe to the later flange.
One more BUT. You said, "my EB runs slow on take off, up hills, those acceleration issues combined with a top speed of 65mph makes me want to improve." The 200 or the 250 will help all of these BUT the 65 mph top speed. That is a result of the 4.56 gear and your tire size. The only solution there is to rev the engine higher, OR change the gears, OR put on taller tires OR all three.
My personal thought on "originaly" - store the "orginal" 170 in case you sell the EB and the new owner wants "original". Put the two barrel on the 200. Don't use an adapter, but rather do the manifold modification as we suggest in our book. (do a search here on the forum for a how to or buy the "book")
If the 250 is also free, get it too. Then you can drive your EB with the 200 as is, while the 250 head is being modified for a 2 barrel and milled off big time for some additional compression. What year is the 250 and its head? Does it have a DSII? Does it have a bell and flywheel? Does it have a barb you could use on the 200? You get the picture.
Good Luck