ok it is a bit hard to tell in the photos you have.... try and take some extreme closeups
best way to tell for sure would be to take a closeup photo of a few of the phylodes.
It took me quite a few tries to actually find obtus in the wild but as soon as I saw them I knew...
you are definitely on the right track with the leathery texture... obtus are very noticeably leathery textured compared to similar acacias like longifolia...
also keep an eye along the edge of the phylodes... all obtus will have rough edges with little chunks taken out... this is due to something that happens when they are in the bud stage... cant remember exactly what, Im quite the amateur botanist...
please keep in mind when working with most of the active acacias... try not to harvest a full tree... use recently dead trees if you can... but if not, the phylodes DO have a relatively high percentage of DMT... if youve found a grove of younger tree's just strip some of the phylodes from each tree... maybe prune a few branches as long as it promotes more growth... really try not to kill a whole tree... if you only take some phylodes and do a little pruning you will ensure that they can grow back by next season and you will have a continuous supply for ever
Im not thinking you were planning to go and kill any acacias... but it is something I have been thinking about lately and thought it wise to post on a public forum
good luck