When I got my ute engineered the process was you fill out the modification application with what you want to do they will send you back a letter saying that you can do it and what standards it has to meet with a list of engineers yours shouldn't be a problem with A15 with twins. You are better of getting the Tech section to tell you what testing it has to pass.My engineer wanted mine to do emissions test we argued for a week or so rang tech section and asked about it and said the test is not listed on approval letter you dont have to do it. Which was good I didn't want to spend up 2 grand at Kosteci's. With engineers cert guys at pits didn't bother driving it just had to wait 3 hours to write report
This was in 2008 the engineer was $440