Thank you all. Great ideas. The Harken furling manual - and it's so old that it comes as poorly type-written sheets, stapled together - does refer to an extra block if required to get the correct jib halyard sheeting angle. I'll review that. I have more to learn about "cranes" for spinnaker halyard blocks. I should just sacrifice the lovely jib halyard splice and remove the snap shackle - one friend and "expert" just ties a bowline, no thimble or splicing, and has always had that work (speaking of "NASA" solutions). I have to document which of my sails are too long and which too short (on the luff) and have them adjusted. (And I could try to understand why that's changed from last year ...)
I don't normally use multiple foresails for our "casual" club racing - and to do so would have to remove the upper part of the furling mechanism, which is not impossible, but a bit of a hassle.
(For clarity: my problem was both with the jib halyard shackle releasing and with wearing through the spinnaker halyard [and that on occasion interfered with furling the foresail].)
Thank you again. I may be back about this!