I'm not sure what you are refering to when you mention "injector" or why petrol would be going into the oil? The car will have just one injector, which will be in the throttle body. The pipes you see above the cam is an oil spray bar to keep the cam lobes lubricated.
If one or more rockers have broken, it's a fair sign that either something has been sucked into the the engine (e.g. stray nut or bolt), or that the cam timing has slipped due to a broken or loose timing belt. This can cause the pistons to hit the valves with a lot of force, certainly enough to snap those rather spindly looking rockers. If this is the case then you are probably looking at bent valves as well, which will require cylinder head removal, and maybe even piston damage which would be expensive to fix. Does the timing belt look in good condition and properly tensioned? Does it look like it's been recently replaced? Check the valve timing before attemping to run it again.
Looking at the design it's also possible that a follower could get displaced if the valve clearance was excessive.
How much damage has been caused to the cam and surrounding areas? Have you managed to retrieve all the bits of the broken rockers? If not they will be floating around in the engine somewhere, hopefully in the sump and will need to be found and removed.
It looks like an easy engine to work on, but fiat parts can be quite expensive. If you have all the broken parts, if you can pick one up cheaply it may be worth getting a second hand head and swapping the cam and followers over, then doing a compression test. If a compression test shows low compression, then the head will need to come off to check for bent valves and any piston damage.
If all else fails, I suspect a s/h engine from a breakers won't be particularly expensive.
