Hi...Making a sideplate is quite easy and one has a better chance of making a sideplate that looks like it's supposed to be there. Of course, some originals have sideplates that are mainly used as a washer and don't particularly look well placed .
Buy a sheet of 1/8" thick brass and clamp it to the SP panel and through the 2 lockbolt holes, use the shank end of the same sized drill as the hole and make it into a centerpunch. Tap the drill in each hole and use the prickpunch to circumscribe dias on the brass....you can then layout your design from these circles. The tail of the SP should center on the rear of the lock panel , but the SP "nose" is already located. In between the 2 holes, an attempt can be made to make it look like it "belongs"....good luck.....Fred