So I've been trying to find the answer to this, but maybe I'm just using the wrong keywords...
Are the header ports the same size on a 3.4 as it is on the 2.8? I installed some WCF Long Tube headers on my 2.8 but still want more power (isn't that how it always goes?). So I was looking around and I know my intake will fit, but I don't want to just lose my headers.

The 3.4 has identical heads to a HO 2.8 Headers are interchangeable. Good luck!

If you're talking about the iron-head 3.4 V6 (i.e. the Camaro / Firebird engine), then the headers will fit... because the 2.8 and 3.4 use exactly the same cylinder heads.

As a matter of fact, I did exactly what you described when I replaced my dead 2.8 with a 3.4 crate engine.

all the 3.4 info you could need is in my swap thread. link in sig

But yes they use the same heads.

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"DRIVE IT LIKE A FIERO"
'84 Fiero, engine to be determined
'87Blue GT 3.4L Swap Completed!!!!!!!! Boosted!!!!!!!
^^^^ Now in the Construction Zone^^^^
Las Vegas Fiero Club Parts/Sales/Service/Club
Fiero Road Club Of Northern Nevada

Thanks so much! Now I just have to get the money to actually shop for a 3.4... that might take a bit.

quote Originally posted by FieroAndrew: Thanks so much! Now I just have to get the money to actually shop for a 3.4... that might take a bit.

About ten years ago when I installed a 3.4 OHV in my Fiero, I was able to score a "low mileage" (60,000 - or so they said at the junkyard) 3.4 out of a Camaro for $500.00.
With the cost of the motor plus the necessary gaskets and a couple other small items, I was able to do the swap into my Fiero for just under $800.00 (actually, it was about $780 IIRC). While the motor was out, I took the time to gasket match every intake/exhaust port, took the heads apart and cleaned up the bowls, replaced the old valve springs with new aftermarket springs, added 1.6 roller tip rockers. It was pretty easy, just allow yourself some time (assuming that you already have the tools to do the job!)
Chris