This is a useful mod. I would suggest adding the ability to change a couple of results or add an alternate coal synthesis recipe as a toggled option. I have been messing with trying to make all the science packs on a Fulgora start and the problem ends up being that there is nowhere near enough stone to make appreciable amounts of production science. I was running with 10 solid fuel + 100 heavy oil + 1 sulfur + 100 steam → 5 coal.

To make 1 set of science packs from 300 scrap and have a reasonable amount of surplus for building you need this setting.
24% Gear, 6% Solid Fuel, 6% Ice, 6% Steel, 4% Battery, 12% stone, 4% Adv Circuit, 6.8% cable, 3% CPU, 2% LDS, 1% Holmium.

I kept holmium as the conserved drop rate. Though I expect most people will increase it.

If you would like me to run other numbers I would be happy too.

Thanks a lot for testing this so thoroughly and for posting the numbers!

Good news: you can already use your setup with the current version. Every output has its own startup setting, so you'd set:
Gear 24, Solid Fuel 6, Ice 6, Steel 6, Battery 4, Stone 12, Adv. Circuit 4, Copper Cable 6.8, Processing Unit 3, LDS 2, Holmium 1, and Concrete 0. Concrete isn't in your list, and an output set to 0 is removed from the recipe entirely.

That adds up to 74.8% (vanilla is 60%). Since it's under 100%, the mod keeps the vanilla behaviour of one roll per scrap: each scrap gives at most one item. Only if the total goes over 100% does it switch to independent rolls, where one scrap can give several items. The exact expected items per scrap is written to factorio-current.log at startup.

About the coal recipe: I'd rather keep this mod focused on the scrap recycling recipe, so a coal synthesis option probably doesn't belong here. I'll think about whether it's worth a small separate mod.

When you say "change a couple of results", do you mean swapping outputs for other items (e.g. coal or something not in the vanilla list), or something else? Let me know and I'll see what fits.