L76/6L80E install questions

[1967wannabe]

Finally got my L76/6L80E combo stabbed with CPP mounts & stands and need some opinions.
1) I'm planning on a custom drive shaft so I see no reason to leave the motor so far forward, there's a ton of real estate between the motor and firewall, any reason to not move the motor back 4-6 inches?
2) I've seen the 5.3 truck motor with CPP mounts in 67-72's use the factory LS compressor & mounting, mine almost fit, I'll have a little more clearance once I move the motor back. Is the compressor mounting the same on the L76 as the truck LS?
3) The alternator also almost fit, 1/4" less frame rail and it would have slid right in. I plan on trimming the top of the frame rail back about 1/2" to facilitate the alternator as I like the accessories mounted low. I don't want to weaken the frame but it's already much narrower back by the upper control arms so I don't see how 1/2" trimming with affect the strength of the frame.
4) I've heard two opinions on the LS a/c compressor working with a Vintage air unit, anyone know the truth?
5) I had to pull the oil pan as it hits the crossmember, it's a Pontiac G8 pan which looks like a CTS-V pan, pretty sure it'll clear just fine if I move the motor back.