Yes, it can be pulled through the hatch full assembled, less carb. With mine, I took out the passenger front seat, the couch and the table and chairs. I laid down a tarp, and then laid plywood over the top of the tarp. This protected the carpet. When I brought the engine through the door, I put plywood on either side, so the engine could flop around without damaging the door frame. I used to have a website with a bunch of pics, but now only have some photos left over on Photobucket.
https://s213.photobucket.com/user/Davei ... t=3&page=1I modified the engine hoist to raise the legs up over the front floor. Once pulled, I was able to roll the hoist back far enough to set the engine down on the main floor. Then reset the engine hoist legs, picked it up and rolled it back as far as I could get it. The put the engine hoist on the ground and hooked the engine through the door and brought it out. Its a bit tedious, but not unreasonable. Yes, the 502 is a drop in for the 454. Some minor grinding on one of the engine mounts to clear a nub on the block, and modifying the pan to fit over the diff. The modification to the pan was just done with a sledge hammer. Never took the pan off the engine, just pounded a dent in it, so it would clear the diff. Easy to do. I used the 502HT, but then added port fuel injection and headers. When it was all said and done, I figured somewhere between 420 and 440 HP. From a 20 mph roll, you could punch it and light up the front wheels. If floored, it would chirp going into second at 50 mph. It would also hold 80 mph up a 6% grade towing a 4500 lbs Grand Cherokee.
I did a number of other modifications to it, such as rear disk brakes, Koni FSD shocks, Tapered roller bearing bellcranks. Also build the differential so it wouldn't break teeth when it shifted under full throttle. Also dropped a 4L85e in, but that was a whole other project. Not too difficult, but requires moving the trans mount and lengthening the driveshaft. All do-able from under the coach. It was a blast to drive, as you could treat it like a car. When I sold it, I decided to break the 100 mph barrier. After doing so, so idiot in a pickup cut right in front of me and used up all my space that I was anticipating between myself and the traffic I was catching up to. Even at 100 mph, slamming on the brakes, I never had any brake fade. It just braked hard. I can not imagine doing that in any other coach.
I do have some advice. If you go with a 502, go ahead and get the 502/502. If you are thinking of fuel injection, just get the ramjet and forget about alternate after market kits. In the end, you won't spend much more, and it will be simpler to deal with. The important issue with the 502/502 is that it uses a fast burn head. This will significantly improve mileage. You could also drop a 496 in it, which also will improve mileage, but won't have the top end. The 502 just screams.
Go to the trouble of installing disk brakes on the rear. You can get a direct fit kit for the Dexter 8K lbs axle from ETrailer. Drum brakes use the rotation of the drum to increase the braking force. This means there is a delay before you get full braking with drum brakes. Disk brakes are instant application. You don't realize how much difference this makes until you make the switch.
If you tow, a rear trac bar will make a world of difference. If you do not tow, you don't need it, but if you do tow, it gets rid of the massive understeer.
The Dana 70 running in reverse has a reduced torque rating. As such, under high torque, it spreads the pumpkin, and which allows the ring gear to loose mesh with the pinion gear. Not only that, but the movement puts wear on the carrier, and eventually the pressed fit bearing race moves around and eventually wears out. Carl Jantz can fix this. He adds bearing girdles which are mounted through a heavier cover. This stabilizes the bearings so they don't walk around and mess up the pressed fit on the carrier. If you Google his name, you will find him. He is a good guy and knows his stuff. He has a hobby of off roading, and has made a business out of custom products for his off road buddies. HE also won the Alaska Off-Road Warriors a few years back.