I have bought a world models cap 120. The instructions recommend a 91 2 stroke or a 120 4 stroke for this model. I was going to power it with an o.s. 91FX. Do you think that this will be sufficient power? As I don’t want to spend money on a new engine and it not get the full ability out of the plane. If you aren’t familiar with the model it has a 73 inch span.
Also what prop size would you recommend for this model?

Thanks for your help

If anyone has a similar sized cap or Extra, what do you use for your setup?

Saito 180 or OS 160FX are pretty common choices. I wouldn't try a 91FX on it.