There have been a few threads about the Big Daddy and possible mods - so I thought I would share my story.
A few years back a local hobby shop was going out of business and they had a really good sale - so I bought 2 Big Daddy's (along with a few other items).
I came up with this idea of extending the Big Daddy body by coupling one and a half bodies together. I used the remaining half (with the fin slots) and made a tube coupling. And the remaining nose cone? I made a boat tail.
Then I added a 29mm motor tube along with some plywood centering rings.
Here is the portrait:
I named it the Pater Grandis, which is Latin for Big Daddy.
Here is the business end:
The motor retainer is a pair of washers and nuts on a threaded rod - which goes all the way through the three centering rings and secured at the other end, thusly:
(Apologies for the slightly out of focus photo). If you squint, you can also see two eye bolts, with a bit of aircraft cable between them, attached to a bit of tubular Kevlar.
I've flown this rocket quite a few times on mid-power motors. It is a great flier, but it's been scuffed a few times on the playa. I hope to be flying it again soon. Unfortunately, I lost all my documentation along with a computer crash I had a while back (a good idea to back everything up periodically), so I'm going to have to try to work out the best motor for it all over again. It weighs in at 27 oz unloaded.