Hello,
So i came up against this problem today for the first time where i had a cam retard of -18 on a 2000 4.3 and discovered that the distributor is non-adjustable. I searched for an adjustable distributor but didn't find one. So I went and looked in my bolt bin and found this battery hold down and a M8-M45 bolt....

I simply placed the battery hold down on the intake and the distributor hold down on the top step. Used my scan tool to adjust the cam retard to 0 Deg. Engine runs great, no codes, the distributor is solid and doesn't move at all.(better yet, the dizzy is now fully adjustable) I hope this might help someone who has the P1345 and needs to make a timing adjustment.
Thanks,
Fixxer