Yeah.. junk wise it *really* makes sense to put scrapheap near Boneyard, since the town already scavenges for scrap materials, especially Gun Runners, and like most of the nearby area is already pillaged out of all usefull materials, so scavs have to do trips far beyond town to fetch something usefull, and you propose to setup a town made of "precious junk walls" in remnants of L.A.
dude think agin..
Scrapheap would be literally stripped apart if it weren't for those gangs fightig for control over it, so residents willing to get rid of the gangs fail logic here..
setting Scrapheap in place of Necropolis is also dumb since nobody wants to re edit the map and all random encounters just to put a small meaningless location there, and as you said too late for getting dogsh!t, not to mention Necropolis would be moved to the desert, where supermutants are frequent in random encounters.. meeting a random encounter with supermutants is a suicide without some PA, unless Lexx would wrote a script that if dude and his humanoid party is wearing cathedral robes the supermutants would not turn hostile. otherwise You'd be forced to do BoS questline to get PA..
You'd most likely be outta time before you manage to do everything.. unless.. unless Lexx would decide to kick dogsh!t outta scrapheap and place the motorcycle there, as a main reason to quarrel betwen the gangs.. and if you take out both you'd be alowed by townfolks to take it as to not draw attention of more wasteland scumm, perhaps some fixing should be required with nessecary parts split between the gangs, i.e. crypts have the cell controler and fools have the schematics and none of them have the nessecary tools or knowledge to fix the bike, ofcourse the bike would still require to fill it up with charges.
As things are now i usually manage to get the waterchip with ~83 days left. because I loose around 48h to get the bike for seat upgrades in Boneyard ( a.k.a leave Tycho in Necropolis, travel to L.A. for bike upgrade +pickup Katja+ Hydroponic part quest+ initial GunRunnr shopping+ Smitty upgrade, return to Necropolis pickup Tycho, go to Vault 13, hand out water chip..)
Frankly without the bike or the random encounter mutants non hostile to CoC robed party i don't see how else you'd manage to deliver the chip in 150 days..
It would require getting the PA so straight to BoS for glow quest, go grab radX to L.A. Followers, go to glow, back to BoS, and you're left with ~50 days or so, then dressed in PA go to Necroplis on the desert somewhere west of Lost Hills, litrally own everythig on necropolis due to how op you are, get the chip, and fail to manage to get back to Vault 13 with water chip on time.. so pretty meh...