[willy]

Mainer a few suggestions and some will disagree but if I had to do it over this is what I think.
1. Do not, I repeat do not put a heavy motor on the back of a V20 with a bracket. 150-175 max and the lightest engine you can get.
2. If you get a bracket make sure it is the kind (whatever brand there are at least three good ones out there and well made) that has flotation built in to counterbalance the weight further back on the boat.
3. Get a full width bracket, the kind with the sides like MJ's, more functional and will let you stand back further to pull line or debris off the prop etc, also get the folding ladder with it.
4. Get the shortest one that will let you fully tilt your engine out of the water at rest and no farther.

In reference to #1 this is my thinking, I have been on two V20's that were otherwise sound boats that had a bracket and a heavy V6 motor, they all dunked their engines in a heavy chop on a drift or when coming off plane even. They also tend to porpoise in certain sea conditions and put a lot of stress on a transom. If you tow or trailer your V even more so and it is hard to rig an effective transom saver for them.
Another little tid bit. I had a 115 4 cylinder Johnson on my V with a thirty inch set back bracket. That puppy got 35-37 MPH with a full tank of gas and three guys along with all fishing coolers etc. and a bimini with front curtain. It was an absolutely perfectly balanced boat on the water and never dunked the engine in any condition or drifts thru the rips. The bracket on these boats adds excellent performance boosts and putting a heavier than needed motor on it won't due a lot for you.
In my opinion a 150 two stroke like the ETEC would be ideal. Performance will be in the mid 40's loaded up. The gain beyond that will be minimal with a lot of trade off's, none good.