I am no expert but on the plus side I believe the Lancia Beta rims are 14", 4 x 98 and magnesium alloy making them very light. On the negative side they are a front wheel drive not rear wheel drive offset.
Correct on all counts!
The wheels are extremely light magnesium alloy and they are 14 inch and 4x98pcd so a straight fit on the Fiat 131. My car is fitted with the larger discs (and callipers) from a Fiat Bravo so 13 inch wheels won't fit, they must be 14 inch (or larger). To counteract "the negative side" of the incorrect offset, the wheels are mounted with solid alloy 8mm spacers. But that creates another problem as the rear hub-centric ring is just 8mm so with the spacers fitted the wheel effectively sits flush on the hub and spacer. Perhaps I should have replaced the wheel bolts with studs and nuts but I decided to use high tensile steel bolts instead.