Fountain 35 lightning
done with bravo drives, should I go with the scx4 or ssm5?

How much HP?? If under 800hp, I'd go with SCX's uppers mated to SC lowers.

I was at 771 with NA 572
but I pulled them and I am building a set of 14/71 blowed 572
should be around 1000-1100

I have been looking for a set of the 7m arneson or a set with drop boxes but I have about gave up on that

I'd stick to the SCX's and get a set of drive gaurdians. I've been running them with 950 horsepower for about 200 hours without issue. I have the mercury sport master lowers and they have been fine too. The drive gaiurdians help with any shocks from jumping the boat. If the lowers are a concern of yours you could look into IMCO's new dual down shaft lowers. They would be more than strong enough and possibly a little faster than the sport master or sc lowers.