Good to hear your still alive and kickin!
When I look back to my best training I did strictly for a thon was Pfitz advanced marathon on the 70 MPW or less, and I became very good at holding a pace, I was slow as shit, but I could go longer. A lot of it was those Med-long runs. I ran the marathon at 6:50’s that year and ran all those mid weekers 12-15 miles at 7:50 -8:00 min pace. Didn’t even know why at the time did it just because Pfitz said so 😉 I would cut out an easy day or take a day off on a short run day vs. missing a mid-week long run even if it was at a 9:00 pace. Soo to answer your question I think it would hurt your training if it’s for a thon