Crane H-272. Valve lift is .454 intake; .480 exhaust.
It probably requires machine work for valve spring clearance, to prevent coil bind. (There may be some springs that won't bind, but you'll need to research. I couldn't find any when I did mine.)
I used Comp roller tip rockers. 1.52 (stock?) ratio. Didn't spring for the full roller rockers.
If you don't want to deal with that, then the H-260 is probably the biggest cam that will fit. .427 intake; .454 exhaust.
Note that Comp Cams also advertises a "260" and a "272". They are not the same as the Crane.
The Comp pieces have equal intake and exhaust lift, while the Crane pieces have "staggered" specs, similar to the stock Fiero cam. (Stock Fiero and 3.4 both have the same specs. .394 / .410, I believe.)
There was also an Isky cam with similar lift numbers to the H-272.
I used a Cloyes "true roller" timing set. It allowed the cam to be advanced or retarded, relative to the crank. I installed mine "retarded", to help with the top end, since the 3.4 has tons of torque. (I also had the heads and intake ported, headers and bored out throttle body, to help with the breathing.)
One of our former members built a similar engine, but he also had the heads milled for higher compression. As an alternative, you can use the 3.4 DOHC pistons.
The 272 cam calls for "higher compression", but I didn't do that, since it had always pinged with the stock cam. In retrospect, it probably wouldn't have hurt. After all the mods, I was able to run 10-12 degrees of initial advance and still run regular gas.
As always, YMMV.
Edit - I have a sheet, somewhere, that lists over a dozen cams for the iron head 60 degree V6. I'll see if I can find it. It's been a long time, however.
