Mixed ANOVAs in SPM

Dear NeuroStarts community,

I would really appreciate your support here:
I have a mixed design with between (Intervention) and within (timepoint, stimuli) subject factors. The idea is to replicate a previously published manuscript (with the same task and design) that computed the delta (difference between timepoint 1 and 2) and then, performed a repeated measures with the resulting contrast images. My question is: Is this approach valid? I am taking the contrasts from the first-level (t-test), compute the difference (Timepoint 2 - Timepoint 1), and then take those images to a full factorial design on a second level with Intervention (3) as a between subject factor and stimuli (2) as a within-subject factor. My fear is that I omit important information regarding the within-subject variance in this way.
Is this correct? or should I perform one within and one between separate ANOVAs with this images?

I hope you can suggest me something,