Most "tells" are in the interior. The IM is closest to the real thing with a roomier floor area and a low, squared-off tunnel like the real Speedster. Dash trim is pretty much the same as the real ones unless the owner has requested something different.
The Beck has a wide, flat floor with enough room on the passenger side to rent out as an efficiency apartment. There is no "ridge" next to the door as in the others. The floor is flat all the way across except for a low, squared-off tunnel like the IM. The dash trim includes the roll but usually does not include the bright metal strip unless the customer requests it. Door top trim is squared off, unlike the originals' rounded trim.
Vintage and JPS are almost the same inside unless custom stuff is ordered by the buyer. Neither has the dash pad (or roll - not sure what to call it). In the JPS the dash top leather/vinyl dash cover extends to the doors while the VS cover stops an inch or so short. Both have narrower foot boxes as they are based on the Beetle pans. They also have taller, more rounded tunnels. Door top trim is square.
All of these have emergency brakes on the tunnels rather than under the dash as in the real ones. There have been some IMs and Becks made with under-dash e-brakes as special requests. Probably the same for JPS and VS, but I am not aware of them.
For Speedster the shift knob, switch knobs, and door handle bezels should be ivory, although many are black unless ivory is requested.
Outside "tells" are a little more subtle. Trim variances were common on the real ones, so the lack of side trim is not really an indicator. The Becks have bumpers that are a bit thinner in cross-section and that stand out a bit more from the body. Until recently the standard Beck deco molding was different, but I believe they use reproduction trim that is much like the originals now. The style of license plate light and tail light should be as follows IIRC:
- Beehive tail lights with shine-down license light through '56 (I believe)
- A short period of some with teardrop tail lights and shine down license lights in early '57 as stock of parts was used
- One shine down lights were used up in early of mid '57, all 356A cars had teardrop tail lights and shine up license lights
This last bit is from memory and that has grown increasingly unreliable over time. Sigh...
Wheels should be 10-slot wide-5s with baby moons, but variances are common. Most replicas have 8-slot rims due the use of 4 lug hubs, but some Becks have custom made 10-slot, 4 lug wheels.
I think Real Speedsters all had bumper over-riders, but most replicas do not.
That's all I can think of at the moment.