"2 bbl FiTech?!" Damn, I should have waited!
I installed a FiTech last month (slant 6). New offy 4 barrel intake. (Maybe wouldn't have needed that if they had the 2-barrel available!)
Return line: FiTech does not require one for my application, but I remember 90's TBFI cars would get vapor-lock issues! (I drove one with that vapor lock issue.) So I decided return-line was the way to go. I re-purposed the existing hard fuel line (5/16") and added a "3/8" (-6 flex-line zip-tied to the hard-line) feeder fuel line (unregulated). The FiTech instructions said I needed a 3/8" fuel line but I could use the 5/16 for the return. (WAY WAY overkill since I'll never flow that much fuel, but whatever, I was adding a fuel line either way.) One of the things I liked about the FiTech is that it will intelligently control the fuel pump speed. (Not sure about other brands.) I went with an in-tank fuel pump... allot of extra work. And the in-tank FiTech kit does not come with the fuel line, so that's a bit of a hidden extra cost versus the most basic kit. The most basic (least expensive) kit has an in-line fuel pump but in-line pumps must be mounted BELOW the fuel tank! I didn't want that thing being the lowest thing hanging under the car. The easiest option would be their fuel command center, but it's big and goes inside of the engine compartment.
The tech support guys were good and always answered the phone. The Holley rep I talked to said FiTech was known for not having support after the sale. Not my experience.
Oh, and this might apply to other brands, I had to install a bigger (3/8"? NTP?) "GM-style" water-temp sensor. This requires drilling and tapping a bigger thread into your head. I didn't like that. It might be possible to find a water-temp sensor that will screw right in the existing hole (1/4" NTP?). Anyway I found a water-temp sensor online that had specs that 'looked about right' but then when got it I did some resistance measurements. It was not as closely matched to the FiTech sensor that came with the kit, so I chickened out since I want the thing to work right the first time.
The Oxygen sensor hose-clamps that come with seemed way too whimpy so I found some good heavy-duty stainless-steal clamps on Amazon. (Eventually I plan to just weld the bung onto the exhaust.... but I figured I can do that later.)
Idles like a dream... I haven't had it on the road yet since it's been too sloppy (Minnesota). I'm hoping to take it for a maiden-voyage spin this weekend if the weather cooperates.
O-rings: the in-tank fuel pump has a built-in regulator and comes with a plug to swap out if you use the return-line configuration, as I did. (Again, you don't *need* a return-line for my application.) Anyway, the plug had pre-installed o-rings that were just wrong. I swapped those with those that came on the regulator that I was removing. Now it's fine. Though that was 'sloppy' of them to ship it that way. It would have been better to ship the plug with no o-rings so one would naturally grab the ones from the unused regulator...