Marathon and ultra are different paradigms, for ultra all you need to do is get a heart rate monitor and try running at zone 2 as long as you can, the most difficult part is probably refueling, eating enough calories while preventing stomach cramps. Marathoners chase speed cos 42km/26miles is not that much if you are acclimated, which leads to a lot more interval/tempo/threshold training.

Ultra typically has much more vert, if you don’t strength train or train downhills your quads get destroyed. It gets to the point where you want uphills because the downhills are all pain.

It’s also not unusual for ultramarathoners to include speed work early in a training block (see Jason Koop).