Hi,
With the euro transom, doesn't make sense to me to have them on the transom - I know duh - had to say it. It is the best location on a boat like the Gulfstream.
I would consider them on the gunnels aft of the aft rod holer. I think you are ok on the port. On the starboard there is a breaker for the shore power I beleive. You need to have enough room. There is room further down, but the outriggers won't be in the same place (not a big deal to me) unless you move and rewire the breaker.
I had a pair of Scotty 30" manual strong arms on a boat. I used the square swivel mounts that allow you to remove the outrigger and all that is left is a smooth mounting plate. As stated, I would not use the gimbal mounts - maybe if I had transom rod holders as the stress would be on the body of the rod holder not the pin.
You most likely will be placing the arms perpendicular to beam and there will be stress on the pin inside the gunnel rod holder. Take a look at the pins in the rod holders - not very strong and not made for this application in my opinion. The other consideration is that you don't have to use the rodholder on the downrigger - you can use the rod holder in the gunnel right next to it.
I would use all SS mounting hardware and those black or white phenolic washers above and below all washers. use SS nuts with nylon locks as well - maybe 2 on each bolt. Use a PT 1/2" plywood or an aluminum backing plate so you have something to support the under gunnel mounting points. Seal the hole insides as well as all mount points with 4200.
