Possible Soft-Brick Fix for my Galaxy S4
Try disabling verification, via safestrap, and try both methods + Sideload again.

I should ask, why heimdall and safestrap? Use Clockworkmod recovery instead of safestrap and ODIN over heimdall. Yes, they require you to get your stuff online beforehand, but clockworkmod has got me out of a lot of soft-bricks

If I was boring, everyone I know would not bother with me :(