LS Harness and AC questions/input

[FAKKY]

Ok - have a read a bunch of threads similar to below. But have a few questions or idea inputs.

http://67-72chevytrucks.com/vboard/s...d.php?t=563063

Truck is a 57 Panel. LS Swap and aftermarket AC
I will be doing a new chassis harness as well.

1) Does anyone make a longer standalone EFI harness to mount say under/behind seat ? Was looking at bp-automotive or painless currently. Sort of also considering the 7 circuit DIY fuse block kit BP offers and using the factory reworked myself.

2) Was looking at a basic cool/heat system. Something like this - any issues ?
http://www.speedwaymotors.com/Vintag...whEaAqwp8P8HAQ

3) Chassis harness think IM going with a rear mount RW harness on this page to free up space in front with AC unit.

http://rebelwire.com/rebel-wire-prod...at=Wire%20Kits

4) What are the biggest tips/lessons you have learned from doing this yourself - stuff you wish you had done ahead of time .... or gone with or thought of.

thanks guys