Use the Boge standard resistance cartos (around 3 ohms) on the slim 510 (and the 2.5ohm Boges probably would not hurt a slim 510 but would use charge up faster. 2.5 ones are hard to find)
Boges look wonderful on 510. If they are thicker at all than the battery it is only by the thickness of the paper covering the carto. I use black cartos on black 510 manuals. If you have a white 510, NiteLiteVapor.us sells white and tan Boge standard resistance cartos.
If you are using the same color standard and LR cartos, you could mark one kind (I use a gold paint pen to mark things - DecoColor brand I got on Ebay).