If I'm understanding you right I'd say that if the tilt/trim and steering on the seadrive works then yes just swap the powerhead and any needed linkage brackets and ur good to go.

for what i was told today by my friend who is a marine mechanic the hear o power unit fit my omc lower unit what i am concern is the steering part witch is connected to the Johnson is short and the omc is long i think it can be change

I MAY be wrong but I believe the steering arm connects to the mid section and not the power head

yes you are right but the part witch connects to the trim/tilt is diffident on the omc

if i add a bracket can i adjust the position of the 20" motor or will it be to low

The vertical shaft!!!! I had the same problem on another boat I had. What year is your motor your trying to hook up to the sea drive? If you go with the seadrive.

The issues with a bracket and a 20" inch motor is constantly swamping the motor when you come off plane.

I guess I'm not understanding something... as far as I know the power head swap shouldn't affect any steering, tilt/trim, shaft length, or anything else below the engine block...... I don't understand why you would be concerned with those things

ok I get it... you are flopping back and forth from using the seadrive to swapping it out for a bracket......

Sure you COULD use the 20" on a bracket but as Kracker said it will be prone to swamping.

The only part I will like to use from the sea drive is the lower part so I can convert the 20" to 24 but by doing that I will have to figure out how to change there is a part under the stearing witch conect the tilt/trim in the 20 is short look at this Pic

http://i1064.photobucket.com/albums/...psd3310c5b.jpg