Heres some pix of what I did in the past...
and I did opt for the welding

 

lower collector was gasket matched

 

what did you use to smooth out the bowl areas on both sides?
[exp: tool and bit]

And were you able to smooth out the entire length of each runner interior?
I tried just about everything and cant figure out which tool would be best. Or at least what type of bit to use

 

I used a rotozip for the big open areas with grinding discs

I used a dremel with a snake attachment for the runners

 

working on getting a big dyno session to test a bunch of intakes/plenums, check out my thread

https://g35driver.com/forums/dfw-g35...take-mods.html

wonder how well mine will do?

 

thanks for doing this write up what good pictures!

i just got my spare upper and lower plenum to play with i am going to fallow what you did