gbernardy:
I haven't heard of anybody else running outboards on the A/O 2600/NSX, but I've seen photos of one and the setup looks nice.
What size cleavers did you try?
I have a friend who has a pair of 300's on a Spectre 30" and I've been in the boat before at 103 -104mph (on GPS), so I would think it should be possible for you to do 100 with the 300x's. the problem with the older 300s was that the rev limiter was at like 6400rpm (the 300x's are 6800 - I think) and it would always bump the limiter with a set of labbed 34" 3 blade Merc cleavers.
I know from experience that the single I/O A/Os don't like a cleaver prop, but I believe on a twin ouboard with a higher X-dim. they should handle fine. You don't mention any handling issues so I take it it ran fine wiith the cleavers?
I would try a t set of Merc 4 -blade cleavers and then experiment with engine height. I think the 4-blades would probably tolerate a higher x-dim which would obviously reduce drag by raising more of the bullet out of the water, as well as generate more transom lift.
I used to own two outboard drag boats in the past, and I can tell you that setup/engine height adjustment with outboards can have a substantial impact on top speed.

Hardcore A/O:
I have been trying to the stats on the cleavers I tried, I think his new ones are 14' 34's, but I can't be sure, I will have more info next week. My friend is now running a Spectre 30". I bought the AO from him. I know my Merc's are 99"s and have the rev limiters set at 6350. I am not sure if I can bump this up, or if it will cause problems. I blew up an engine a month ago and just got the boat back with a new power head in one of the engines. The boat has hydraulic jack plates, so I will play around with the engine height, I will also look into four blade cleavers, I may be able to get a set I can try out and see how much it helps