Port at rear on intake is for power brakes...you will need a new fitting barb to replace the factory push fit one....
Ports at front of engine are emission related....what emission components are you using on your finished build?
Let us know and we can suggest best layout for front ports.
There is a dedicated LS Swap sub forum on our board at
https://67-72chevytrucks.com/vboard/...play.php?f=206
We can move this post over there if you like and you will get much more info....
