The fun answer would be its a moot question and who cares as few would ever attempt this.

Most epoxies marketed for our model aircraft hobby use not a two to one mix but a one to one mix. Mixing the sig stuff two to one would be harder to maintain consistancy from batch to batch.

Use the epoxie on the spar doublers. Very few instruction manuals are going to spoonfeed you through through what adhesive to use on each joint and as you have seem there are choices and opinions on which to use.

Use the epoxie on these critical doublers.

John