I have a center console with the HB 1199.mounted in the console and wanting to replace it with the Helix 12. But they are not the same size. Do they make a adapter panel for this?
Then I was going to move my 1199 to the front of the boat. I was going to move the transducer to the trolling motor. (I-pilot) I do not have any mounting hardware for the 1199 or transducer. Or can I leave the transducer on the back of the boat. Two transducers on the back. Any suggestion would be apprecated.
Or do I just buy a helix 7 for the front and link them together?

The Helix 12 and 1199 are different shapes and would not match up size wise.

You can network the Helix 12 with the 1199 and I pilot link with the 5 port ethernet switch and just use 1 transducer. Using 2 transducers on the transom will create crosstalk. Then you would have to find a clear clean view for both transducers

#1. The Helix 12 takes a bigger hole. How do you adapt for a bigger hole?? You cut a bigger hole. The H12 takes about 1 1/2" wider hole.

Which version of the Helix 12 and which version of the Helix 7?????

There is only one 1199 and that is 1199ci HD SI Combo.

It is not as simple as just stating the Helix model series without stating exactly which one.

The 1199
13.75 W x 9.3 H
All Helix 12 units appear to be the size
14.85W x 8.90 H
I can cut a 1 inch wider hole, but would about the 1 inch gap the top or bottom?

The external dimensions of the units are not always indicative of the cutout needed.
Go to the HB website and download the PDF manuals for the two units. In the manuals there will be a template that you use to do the cutout for dash mounting. Print the templates, being careful that you are printing at 100% size, cut them out and take them to your boat. You can use them to determine if you have enough wiggle room on the face of the console to enlarge it for the Helix 12.

The two units use the same transducer. Transducer Shields and Saver makes a bracket to mount the transducer to the TM. You don't want to just mount the TD to the trolling motor unprotected because the first time you go through a stump field, guess what's going to happen.
All of the input plugs are the same on the two units, so all you have to move are the cable collectors.

If you have a jack plate, consider using a hole shot plate on the bottom and mounting the rear transducer to that. It will get you a clear beam to each side for when you are using SI. I did than on my Seaark and it works great.

The Helix 12 hole has to be 1" larger in height than the 1199----8" vs 7". BIGGER HOLE.