a518/a727 torque converter interchange

Simple question, do they interchange? Lockup for lockup. It's apparently rather close to impossible to find stall converters for the 518 under $400, but Mopar sells just the one I need for the 727 for a reasonable sum of $230.

If the 518's really just a 727 with an overdrive gear, I wouldn't expect the converter to be different. But I've not found information one way or the other. :banghead: