First, I agree with what's been said above. You've made too many simulaneous changes to accurately predict where your motor will sit. .... BTW, if your logs have a round cross section, know that the amount the waterline will move is affected by more than just the weight they carry. If the waterline is near the center of the logs when you add or subtract weight, you will see relatively little movement in the waterline because that is where the log is widest and displaces the most water per inch of depth. But if the waterline is either very high or very low on the log, then changes in weight will produce a much larger movement in the waterline as the log's cross section is much narrower there. ... So depending on where the waterline was on your old logs and how much weight you've added, the new waterline might not be much different.
One more thought - when I needed to change out the engine pod on my old pontoon boat I asked around at the lake where I go and located a guy out in the woods who had been collecting old pontoon boats. He had five engine pods lying about and I found one that was just what I needed. As I recall I bought it for $200 cash. Maybe there's an old boat guy near you.
