Another way to go on this...
That requires a bit of math and a general understanding of wheel offset is to look outside the 4x98 Fiat world, which opens up a lot of different possibilities. 4x100 was a common pattern that came on Honda's, early BMW's, and others. These wheels generally have more backspacing and are designed for FWD cars. You can adapt these wheels to X1/9's one of two ways.
1. Get a set of custom spacers fabbed, which can be made to handle hubcentricity, then use long studs and wobble nuts. The spacer takes up the wheel backspacing difference.
2. Same thing except instead of spacers, get wheel adapters, which will actually transform the 4x98 pattern on the hub side to a true 4x100 pattern on the wheel side. This eliminates the wobble nuts. Same points about hubcentricity and backspacing apply.
Either way, Charlie at Serpent Auto can get you fixed right up.
Pete