has any one installed imco ext boxes with lathem centerd mounted steerring cylinders ? What parts might be needed?

mmm

Why not go all IMCO parts. The arms off the box for the rams are nice. Why mix and match.

the boat is already riged with full hyd steering

Old thread I know, but can anyone answer this?

You need a spacer between the transom and the steering rams the same depth as the extension boxes. I have that on my boat right now. Imco is the best box for a Bravo setup. They use a stock rubber coupler and a torsional drive shaft that absorbs a lot of stress from the driveline. I give that a lot of credit for my trouble free drives.