[Mustang46555]

AMT used to market quite a few different LaFrance models in 1/25th scale. It also looks like Trumpeter is making several now and I recall seeing a Seagrave. You can pick up one of these and use the 1/25th body to make templates, then blow them up on a copier to 1/14 scale. A standard Tamiya tire gives you a good double check of your enlargement percentage.
I've had real good luck using this method to make a 1/16 scale Puma Armored car starting with a 1/35 model. Having the smaller cab will also give you a visual on all the contours of the nose.