the 4.00E indicates 4" rim width, which you'd have a hard time finding affordable tires for, and the E has to do with the bead shape, which won't take radial tires .... 600x16 was pretty well standard back then for any car or light truck, I'd guess 28-30" height
I'd find 50's or 60's 5 stud GM rims, which will be 5", 5.5" or 6" width and then you've got a good selection of tire sizes, radial or bias, to get the right look
Bill
