Brief:
The modification done to this kit originally was constructing my own centering rings and modifying the bulkhead to have only one hole for a single motor configuration instead of placing three motor tubes in the mount for a cluster and a 3-hole bulkhead. This initially didn't fly well, so after another modification I now have a shorter version of the U.S. Rockets Aero Roc 3. It can fly on either 29mm or 24mm motors with the included motor adaptor.

Modifications:
After first flight failed, I decided to saw off the body tube above the new bulkhead, remove the modified bulkhead and motor tube and replace them with the now shorter body tube, the manufactured centering rings, my modified bulkhead, and a 29mm motor tube. I ordered the motor mount parts from U.S. Rockets. The parts package was from what I believe to be the Interroc kit. I had to do some precise lining up with the bulkhead and tubes since there was still left over glue residue from the previous build. It worked out alright I think.

Construction:
The original kit has two equal size body tubes, balsa nose cone, and three fin configuration. Interesting features include a paper canopy recovery and a large payload section.

The PROs of this is you get a lightweight, durable rocket that can utilize 24mm and 29mm motors which could potentially send this baby out there! CONs of this build is it was really not necessary at all. For the same price, you could get an Interroc kit with a four fin configuration and it will actually give you three motor mount options: 1 x 29mm, 1 x 24mm and a 3 x 24mm cluster configuration. I only did this mod because I already had an Aero-Roc and wanted to save money on motor usage. Three motors at a time adds up!

Flight:
It flew pretty straight and true. Very light rocket for the size motors it can handle so make sure you add weight to the nose. It's pretty easy, just drill a few holes in the under side of the balsa nose cone and add some clay or putty, but once again I'd stress saving time and money and just get the Inter-roc rocket first.

Summary:
For rocket modifications, I'd steer clear of U.S. Rockets just for the simple fact that the kits are kind of pricey.