[Dave at Pelican Parts]

The 914-4 cases are all the same, for all practical purposes. That means you can swap the 2.0 crank, rods, pistons, cylinders, and even heads onto your 1.8 case. The 1.8 heads will even bolt up to the 2.0 P&Cs if you want, though I'm not sure what effect that has on the compression ratio.

Note that the 2.0 crank, rods, and pistons all go together--you cannot mix and match between those and the other stock parts. The rod journals on the 2.0 crank are smaller, which means you need the 2.0 rods with a smaller big end, and the length (center of big-end bore to center of little-end bore) is different, meaning the wrist pin hole in the piston has to be a different height.

There are cranks with larger strokes available, though going much over 74mm requires a lot more work inside the case, usually including swapping over to a reduced base-circle cam among other things. With very careful work, strokes of 80mm are possible.

It is generally easier to go up on bore size, at least up to 96mm. As Mr. Tub said above, that on the stock 66mm stroke will give you a 1911cc motor, which is evidently a peppy little beast. Having 1.8 heads makes that swap easier, because you can fit decently-thick cylinder walls into the 1.8 heads--unlike the 1.7 heads, which have a smaller register where the cylinder fits into the head. The kits for the 1.7 get very thin and often have problems.

--DD