SC17 jib block attachment

[dichtbijzee]

The previous owner of our Supercat 17 (1982, with new tramp and traveller upgrade) installed a new jib system complete with a new smaller jib, I think the jib is the selftacking jib size as it doesn't even reach the mast.
But there is no selftacking hardware, so none of the advantages of selftacking with a smaller jib.

the jib blocks are now attached to the front beam:



I have found out that the Prindle 16 and 18 jibs have exactly the same luff length as the sc jib. and we have both jibs to try it with. the only problem now is where to attach the jib blocks.



1,2 and 3 are attached with rivets.
4 is a bit larger and attached with screws.

I have the manual but nothing is shown for jib block attachment in there.

Does anybody know if i can use the larger jib and if so, where to attach it.