Oh pulling the motors are no issue...already had them out and back in...30 mins tops per motor. I see where you think you should be in the upper 80s, but I think the straight bottom and hull design of our boats are going to be limiting you. Also I believe the use of ext boxes is more for the fact of moving weight further back off the transom of the boat for weight transfer and also to get the prop in cleaner water, as well as moving the prop shaft (x demsion) up. I know it be a lot of work but you should try it with no boxes and see what mph ya run then.

My engines were 420s. 40 over 454s with 308 darts, 9.2:1 comp., custom roller cams, 454-r Victor Jr, QF 850s, gil exhaust, all good components.

Haven't dynoed yet so not sure on the power

Ha- no way I'm pulling the boxes to test, if I do that I also lose my steering. It's not as simple as just installing standard transom assemblies. I'm looking to try out a set of IMCO -3's. That is the easier way to go. My issue is I'm still to deep in the water.

If you dig around in here you can find a lot of good info. Somewhere there is a topic from a guy that used to set up race boats. He said in the mid-90's they finally figured out where the X- dimension needed to be and that combined with the new props, that they were seeing big speed increases. He said the stepped bottoms were good for 3 mph +/- but the real increases were coming from x-dimention and prop changes. Also you need a large boat for them to really work. At 29' my boat is just big enough that you may start seeing advantages of a step bottom. Either way, at some point I'm going to try -3's. There are still a few things I can do to gain another 3 mph, but I really would like to get this old boat to 85 mph. If I can get there, I'll be satisfied.