We use a Doel fin on our 25 HP running a 14 ft fiberglass boat. We porpoise like mad at full throttle without it. As it is on the cav plate, it does not force the bow down except when accelerating and then it really just helps with stern lift. We lose about 2 mph at top speed in calm water, but it still runs well. It is a dream in rough water and probably as fast or faster than running the motor without a fin. Boat stability is better with the fin.
If the tilt pin was lost, then it is understandable to try the boat without it. Just be careful when running like that as bow steer causes bad things to happen awfully fast. I have had the tiller do scarey things when trimmed like that. Having our old offshore rig left with the trim down and then hitting the throttle would always get to you if the water was rough. The boat would try to slew to the side before you realized it. Got the gray hair to prove it
Once you get the initial setup correct, you will find a boat is an enjoyable thing. I love the water.
Once you get accustomed to handling the tiller with your left hand, you will wonder why no one told you about that before. The side to side balance will be correct and the boat will handle much easier, especially in turns. Let me know what you think after getting a few hours on the boat while controlling from the starboard side.
I still am in awe of the internet. On a knife forum from England, people from Uragray to other distant points have been very helpful to me.