As to 1) header and 2) jack studs.

I want to widen a 4' wide doorway, to 55" wide.... on a 6" support wall (in the interior, back end of my garage). I constructed the original doorway framing with 4X6 king studs and installed two 2X6 jack studs on each side of the doorway. I suppose two jacks studs on each side is overkill, but I often over-build, as that, since I am not an expert (it passed Metro-Code inspection, so that's good enough for me). The header is a 6X6.

I have a (salvaged) 6X12 header, 7' long. I thought to install this (shortened) larger header. Is a 6X6 header sufficient for the 55" span or does it really need to be replaced with a larger header? If 6X6 is sufficient, then I won't have to trim the cripple studs, above.

Other info:
The ceiling joists above this door, which is floor joists for upstairs, are 2x6s, 16" on center. To date, there is no evidence of the present 6X6 header being insufficient. On one side of the doorway wall, 10' from the doorway, is a 6X12 beam supporting the ceiling. On the other side of the doorway, 12' away, is a **6" exterior (support) wall. The concrete footings are 2'X2' and the slab is 6", i.e., no foundation failure, anywhere.

**On this 6" exterior wall is another 4' wide doorway. I will be, similarly, widening this doorway, also, later. At the moment, I don't recall, exactly, its framing/rough construction (i.e., header & jack studs). The roof profile above this wall is a gable roof.

Also, do I really need 2 jack studs on each side of the doorway, for this additional span? If I can eliminate 1 or 2 of the present jacks studs, this will allow less work of modifying other aspects of the rough framing, as well as the interior wall's finishing, etc.

Thanks.
Sonny