Does an hour of Zone 2 effort cycling roughly equal an hour of Zone 2 effort running?

I'll add one other perspective while we're on the topic since it directly applies to my training. Through a series of trail and error, I've found I simply don't race well above about 90mpw running. I'm fortunate not to get injured running higher mileage than that, but I just don't recover well enough to justify the mileage above that number. But I attribute that mostly to the stress of running itself, not the activity in general. Meaning, it's not like I'm so fatigued I can barely get out the door.

So my goal for a fall marathon has been do add 3-4 hours of Z2 cycling each week on top of my running. But here's the problem that's been discussed, how do you put enough effort into cycling to achieve an aerobic stimulus without hampering the real goal each week which is to RUN to achieve race fitness? For me that started back in May when I got on the bike for really the first time in years. I spent about 8 weeks just trying to get fit enough on the bike that I could get the HR up for a 1-2 hour ride without trashing my legs.

And that was a process, because like a lot of us, I was pretty terrible at cycling. But now that I'm in the heart of marathon training I can still get in that time on the bike while limiting my running mileage to hopefully still get that total work I'd like to see during a marathon build. But the key was getting acclimated to the bike during the "off season" when I wasn't worried about key marathon workouts. I'll let you know how it goes, but at least to this point I'm feeling good about the combination based on what I think my body can handle.

And fwiw, my moderate cycling HR (Z2 or whatever you'd like to call it) is still 10-12 bpm lower than a similar effort while running. But it was closer to 20bpm lower when I started this process. Which probably was too low to expect an optimal training benefit.

This is kinda what I'm trying to parse out. What really is the optimal aerobic training supplement to running, with advantages and disadvantages to each? I'm sure there are differences from person to person to varying degrees. I've ended up going to the Stair Machine because the ARC Trainer wasn't allowing my adductor strain to recover. I've found that the Stair Machine feels good on the legs - the muscles being worked feel complimentary to running without getting them fatigued, and I'm getting my heart rate up into the 130s with that zone 2 feeling to it.