Norman Racing's guess on my 2000 Spica GTV, adding Euro cams and big intake valves, no other changes, was maybe 5-10 HP extra. The IAP cams might add more, but to take advantage of cams you normally need to do other stuff, like mentioned above, porting, compression, etc. It all acts as a system. Also, the IAP cams are likely to add at the high end and lose at the low end, so depending on how you use this car, it might be tough to appreciate.
And the Bosch system is not readily adjustable unless you're a whiz or programmer.
I've got the IAP cams in my 2L and have great power down low and up high but also have motronics, porting, headers, msd, rml dizzy, cut guides, springs of course, and Ingram HP pump, so yeah to really get the most you have to look at it as a complete system. Fun to drive for sure.
The big question is what will you do about fuel delivery? It is easy with Webers. Install whatever cams you like and you will be able to set up the Webers to get a workable solution. Bosch L-Jetronic is not so easy. Contact Alfar7. He may have some cams that will work for you and he will give you the finest after sales support if you are interested in optimizing them to suit your needs.