What side aluminium rods did you use for this build? On the piper site there is only the smaller 250 cubed size.
You can simply increase the rod and pipe lengths in any direction and the printer's size will increase accordingly. If you extend everything by 250mm for example, you will get a 500500500 printer. I do not remember the lengths by heart but I had a calculator uploaded in the Facebook group. I do not have that file with me right now and it will be a couple of weeks before I get back home. If you don't use Facebook, please post a reminder in about 10 days and I will upload it here as well.