Hello,
My understanding is that Phillips head screws do start showing up by late 3A production.  Locations where you might find them on a 3A verses a slotted screw...I have no idea. 

I understand the SEMS bolts to be a one piece bolt and washer.  I don't believe you found this type of bolt on a 3A.

Hi Dinesh,
My 1950 used slotted flathead screws to affix the footman loops to the body.
They were 10-24 x 0.5" and used regular hex nuts on most locations. I can't remember if there were lock washers and flat washers, or just flat washers.

I do know that the 4 footman loops on the tailgate used special acorn nuts to affix the footman loops. They were a stamped sheet metal design encapsulating a nut. I haven't been able to find replacements, but there are solid machined acorn nuts available.

I had to cut many of my footman loops off when I took apart my Jeep, so I intend to use 10-32 x 0.5" slotted flatheads when I put the loops back on.

I also bought a bag of new footman loops from McMaster Carr as they had a great price for a bag of 10 and they are a great match to the originals.

Attached is a photo showing some old footman loops, blasted and primed old loops, and one new footman loop. As well as the hardware.

And generally, going from memory, the only place I found philips screws on my Jeep was on the headlight trim ring retaining screws, and the screw that retains the windshield vent handle pivot nut. That's it! The rest are slotted.

Good luck!

I purchased a Parts Manual that listed all the fasteners used for my vehicle.  It also helped me identify some missing parts.