I guess it depends on how far you want to go with the kit Beans. It is not the cleanest of builds by any means. The launch tubes will need some special attention, much like a gun barrel, they are two part and will have a seam at the joint that needs cleaning up. Unlike a gun barrel, there are many more of them. I have been tempted to replace the tubes with brass tubing myself for the next time I build one of these but I still think you can build a decent kit OOB with a little effort.
Just for future reference though the kit is an M4A3 Sherman, not an M4A1.
Photos of the calliope are fairly rare on the net, here is a link that may be of some help though.
http://www.752ndtank.com/RocketTanks.html
Happy Modelling and God Bless
Robert