Some suggestions that may save you time and frustration...
I started putting together figure #2 first, which is going to be a BAR gunner.
I'm using the sculpt, BAR and M1937 BAR ammunition belt from the Ujindou UD9031 First Special Service Force figure.
Spent an age tightening up the belts and straps to fit the slimmer clothed Marine, then attached the Facepool first aid kit and water bottles. There were no more spare belt holes for the entrenching tool, and I realised looking at the photos that it attaches to the backpack.
That's when the major frustration started!
I wasted so much time trying to get the hooks into the eyelets on the top of the backpack. The second hook just wouldn't slot into the hole. I had to resort to using pliers to compress the hooks closer together, because the eyelets are set too close together. It finally connected, but the problems didn't end there.
The next step is feeding the poncho through the loop on the top of the backpack. That loop is
much smaller than the ones on the sides. Squeezing and holding the poncho as tight as possible, feeding it through the loop stretched it to such an extent that the metal end cap on the strap came off and the strap pulled out of the buckle.
Luckily the strap fed back through quite easily, and the cap can be opened up, replaced and clamped tight again with pliers.
Though there's still the problem of getting the poncho through.
A cunning plan came to mind: wire food bag ties.
I wrapped three ties around the poncho and twisted them to compress it so that it passed easily through the narrow loop, and kept them on until I'd tighhtened all three straps.
The curious thing at the end of all that is that the production poncho seems much narrower than in the promo photo. It's barely lower than the bottom edge of backpack on the sides. In the promo photo it was almost as long again as the backpack.