I rather like Model 1 for the TMP ship and Model 3 for the TUC and TNG ships. I always figured the TOS model was quite different from the TMP model. It seems like the dialog in TMP suggests that the whole system was radically different from the last one. Some have suggested that the big open cargo bay in the refit was the result of the TOS engine being pulled out and clearing up room. Oh well.
Anyway, I actually love how you're incorporating the TMP stuff into the TOS hull though. It's a direction I wouldn't have thought of.