You can make a reasonable assessment of tendency to porpoise from this site: http://illustrations.marin.ntnu.no/h...ing/index.html
I have made some guesses at boat parameters and chosen a very pesimistic LCG. See attached. If it is as far back as 2m then it could porpoise.
If the boat is on a trailer and you have found the ballance has changed it would give you an indication that you might have a problem.
The heavier motors and higher power both work toward instability. Just be a bit careful the first time you do a full speed run. Try to do it in calm conditions and if you find the boat starts to surge then back off. Moving weight forward will help. Trim tabs or power trim should also help but be careful of trimming the motors too far out trying to get more speed.
Other issue is freeboard over the stern at rest.