This "Mk1-Cabin-Hatch" mod add a stock-alike hatch to the stock Mk1 crew cabin's roof from witch you can go and come in EVA.
Forum page: http://forum.kerbalspaceprogram.com/index.php?/topic/151443-12-mk1-cabin-hatch-v010-3-november-2016/
Download link: https://spacedock.info/mod/1038/Mk1-Cabin-Hatch
GitHub: https://github.com/skalou/Mk1-Cabin-Hatch
Module Manager: http://forum.kerbalspaceprogram.com/index.php?/topic/50533-12-module-manager-271-october-8th-better-late-than-never/
KSP Add-on Version Checker: https://forum.kerbalspaceprogram.com/index.php?/topic/173126-180-ksp-avc-add-on-version-checker-plugin-miniavc/