I don't have all the information on this but I told DocM that I would post it on his behalf. Currently in FoolCraft 1.2.2 we are running with 1.4.1 of Simply Conveyors. During testing our 1.3 update we attempted to use 3.0.2 of Simply Conveyors and ran into issues with, I would assume, item IDs. Please see the screen shot here. We would like to be able to update this mod in our pack in order to fix the item duplication bug but are afraid to do so as it would potentially cause issues with existing worlds. The screenshot is from a backup of the Fools of FoolCraft's world.
Any help on this matter would be greatly appreciated.
Thanks in advance.
Jo_Mamm75
Iskall85 Community Administrator
FoolCraft DevTeam

I have a half solution currently, but the thing is currently you lose all conveyors in block form. Only conveyors in inventories update to the newer versions of conveyors.

I'm going to try working on a solution to this today but if I'm not able 3.0.3 will release, which will at least save the item forms of conveyors.

Losing the conveyors which you have placed won't cause any permanent damage to your world thankfully (at least once 3.0.3 releases), but I recommend grabbing up all the conveyors and sticking them in any type of inventory (chest, RS system, etc) so you don't permanently lose them. An update of this magnitude won't happen again, so this should be a one time issue.

But yeah, essentially just wait until 3.0.3 to update the mod, stick all your conveyors into inventories, and things should be fine.

Sorry about the issues you guys are having.

@Zundrel
Thank you for your prompt reply and hard work to update the mod. I agree that this will certainly be more acceptable to people than the alternative. We are planning to try to update multiple SP and MP worlds with our 1.3 update. I will let you know how it goes.
Thanks again,
Jo_Mamma75

Well I have great news. As of 3.0.3 all conveyors excluding the following: Grabber Conveyors, Detector Conveyors, Trap Door Conveyors, Mob Conveyors (their functionality is in all conveyors now), and Downwards Conveyor Ramps will stay in the world in both block and item form.

However, the conveyors will be in the form of Upgrade Crates. These crates can either be broken or right-clicked to drop their contents. In item form these crates can be right-clicked to open individually, or shift right-clicked to open all of the stack at once. They contain the updated forms of the older blocks.

This is due to the fact that since special conveyors have to be converted to modular conveyors (which use modules), I have to give both the conveyor itself and the module. Other side effects from the update from 1.4.1 to 3.0.3 include: Stair Conveyors rotating to the left, Vertical Conveyors turning themselves around, and Fast Conveyors (middle-tier) from previous versions will turn into the Fast Conveyor (top-tier) from new versions.

The update will be out in a couple of hours, maybe less, but I do have to backport to 1.10.2 quickly.

Here's an example of what the crates look like: http://puu.sh/voHim/36e8f31971.jpg

Also note, block forms of the crate will directly put the conveyors themselves onto the ground, but it will drop the modules as items. Some conveyors won't have upgrade crates because they stayed the same unlocalized name across versions.

Fixed in commit f6cf82c.

To make things clear, conveyors will no longer have to be placed into inventories. Things should work just fine!