I am almost complete on the 6 litre conversion into my HQ. I may be able top help out with some information.

Do not use an aftermarket sump, use a camaro LS1 sump, pickup and windage tray, engine will bolt straight in.
( this sump is cast alloy and helps with block Strength )
Try and use and internal pump setup as in the standard LS2 fuel pump. This pump regulates the pressure internally, saves the running of a second Line ( return fuel Line to the tank ) and will prevent you from needed a surge tank set up with lift pump etc.

Castle Automotive parts including engine mount conversion kit fit reasonably well- they utilize V8 HK-HT rubber engine mounts- available over the counter.

Aircon pump will need to be relocated as it fouls on the crossmember and steering box.

Thermostat housing need to be modified to clear steering box also, I have had some of these cnc made.

Hope this helps.