The Alex is not Project G4, though it is sometimes referred to as such. it is project NT-1, because it was built for newtype pilots, specifically for Amuro, but it did not get delivered to the White Base because of the Cyclops Team's attack. G04 and G05 were both stationed on the Throughbred (a Pegasus class warship).
Lost War Chronicles, the manga, is based on a video game. Video Games are hardly ever counted as cannon, and most manga, unless otherwise noted by Bandai is not counted as cannon. Until it's counted in Bandai's official publications it's not considered cannon. Lost War Chronicles, I'm pretty sure is not, but I can and will do a bit of research just to be sure.
Based on technical diagrams of the RX-78-2, I'm fairly certain that the yellow "blocks" on the skirt of the armor could not be used as storage units for a parachute device. Even if said units were storage devices (which by all accounts they are not), I do not believe they would make effective parachute location points. In 08th MS Team we see the first on screen use of two different parachute like devices. The first is in the opening of said animation:




As seen here (I appologize for the wording but couldn't get a better shot) the frist parachute system starts off as a large thruster back pack, then when the pilot reaches the required alltitude to deploy the parachute, it is deployed. The thruster system is obviously there in place to slow the decent further once it reaches the ground for a safe landing, and then discarded.
The second system appears in Episode 09:




The parachute pack is obviously larger and operates a bit differently. Once the three parachutes are launched (they are also larger than those seen in the opening), there is a thruster pack that also rises with it, which once, again, at the proper alltitude, the pilot fires to safely land. Now from what I can gather from watching both animations, the difference in size and design could account for different altitude jumps. Note that they are still in the atmosphere and the ammount of thrust they need to land safely in the second one. Regular thrusters mounted on the RX-79[G] would be a little weaker than what would be mounted on the G-3, since one is a land combat mobile suit and the other was meant for both space and land combat. Also note how the cords are mounted on the shoulders of the RX-79[G].
Now on to the shield. As Miyumi has noted, laying down on some form of protective atmosphere re-entry device is how it is done. This is shown in Z Gundam. I will also show the ballute systems in these next screen shots. Unfortunatly, I can't make screen shots from my Z Gundam DVD's right now, but I'll do my best to illustrate. Instead of using a ballute system like the rest of the mobile suits re-entrying the atmosphere, Camille in his Gundam MK II, used the wave rider known as Flying Armor:

This unit allowed for heat to be distrubuted around the mobile suit and protect it. As you can see there are places for it's shield (can be made out under the gundam itself) and it's hands. In that image it's probably trying to recreate the battle right above the atmosphere, but during the fall through the atmosphere, Camille kept his arms and legs in their propper holdings. Once through the atmosphere the Flying Armor can be used as a support unit to increase mobility and flight.
The ballute sytem on the other hands mount a large balloon like system on the back and larger thrusters on the mobile suit, as seen here on Quattro Bajina (aka Char Aznable)'s Hyaku Shiki:

Now once the mobile suit gets past the point of no return, the ballute automatically deploys, turning the mobile suit on it's back. I suspect that the ballute's exterior for the balloon system is actually made of the same material as the atmospheric reentry film that the RX-78-2 used in the TV series, but there's no information really about what they are made of. Here's line art of the ballute deployed be the Argama. Same as a mobile suit would, but can't find a pic of it.

All of them (except for the argama would would use it's own perpulsion once in the atmosphere) have extra thrusters to slow down their decent. Your G-3 did not. So when you land, you have your basic thrusters that were mounted on the machine when it first left Luna II. It couldn't have slowed the decent enough to even come close to safely land. I've already covered this in the other topic. The atmospheric re-entry systems of the RX-78-2 (and possible similar counterparts) were not meant to allow the entire suit to land safely. This isn't Getter Robo, where it can just leave from the moon and crash, landing on kneeling on one knee and the only thing different is that it's red paint job's been burnt to black. The Gundam, being a real robot and not a super robot, would have plummeted to the ground, and if they pilot did not escape using the core fighter, he, as well as most of the Gundam would be crushed. The whole 9 meters per second gravity thing comes into play.