I confess to being bit confused by your question. The Z2 base work is critical for success in long events. However I would normally recommend just adding more easy volume to the weeks in the plan if you feel you handle it. It sounds like you extended your base period another 2 weeks. Nothing wrong with that. I would not cutout the gym ME from the plan. I question the wisdom of doing another race 2 weeks prior to the original planned date. Because you will need to taper for that race and then need some recovery time afterward. Both of those cut into valuable training time. If I am missing the point please add more detail.