Volvo gear ratios
 

I have a 29 ft. flybridge cruiser that I am building a Volvo AQ style duoprop drive for. Stock weight is 8100 lbs. Fully loaded I think it will be 9500 to 10,000 lbs. I had originally anticipated putting a 330 hp. 454 in front of it. I recently came across a 502 Mag Mpi 415 hp. that I bought to use instead. I already had acquired a 1.78 ratio lower unit to use when I found this engine. While recently looking at some older Volvo literature that I had, I saw that with that horsepower engine, they were using a 1.68 ratio. My question is will the 1.78 be okay in this situation with this heavy of a boat or do I really need the 1.68? Thanks in advance for any input!!