Nothing has really changed in the many years that people have been trailering a Gulfstream... or trailering, in general. Here's a search with plenty of reading info:
https://www.greatgrady.com/search/1627179/?q=gulfstream+trailer&c[title_only]=1&o=date
You can get the weights/specs from GW's site and calculate the boat weight - then add the engine weight, which is all findable online. Probably about 450 per engine (give or take). Point is, calculate it yourself so you KNOW it's right.
If you go with an entry level trailer like a Venture (be careful with those, though... they're kinda hit or miss for quality) then it might not be a bad idea to add at least another 10%.
Edit: Forgot to add... if you're going to do all the adjustment of the trailer to fit your boat yourself, make sure you do all the calculations yourself as it's all on your. Total weight and distance from garboard drain plug to bow eye are the two main ones.
However, if you're going to buy from a dealer then they can do the adjustment, too - it shouldn't be too expensive to just let them do it - maybe 2 or 3 hours tops.