From 20' away, one just needs to look at the windshield wipers. Most replicas come with the VW wipers rather than use the thinner wipers of the originals. Then there's the wheels. Some speedsters come with 4-lug wheels. You will be able to tell by counting the slots that surround the hubcap, if one is on. There will be 8 slots or openings. The 5-lug wheels have 10 slots or openings.
Where the replicas start to fall short visually as compared to the originals is the interior.
1. The top. The original was a folding top that did not snap in place at the rear. The tonneau snapped in place using Tenax fasteners. Fabricators such as Vintage and JPS (and I believe IM) snap the tops in place using button snaps, as opposed to the Tenax fasteners.
2. The parking brake. By far the easiest giveaway for a replica. The originals had the umbrella handbrake under the dash, as opposed to the handbrake in the center.
3. Dash. A few areas of difference, depending on the replica maker. The gauges on most replicas tend to be oversized by a few millimeters. I know it's only a few mm, but once you witness an original, it sticks out. A number of replicas have the speedometer on the left, when the originals had it on the right of the cluster.
4. Dash Pad. VS and JPS do without a dash pad. IM and Beck have a rolled pad. In the original it's more flattened. Also, VS and JPS do not meet the top of the door like the original.
5. Door. The top of the door card is rounded on the original, similar to IM and Beck. On VS and JPS, it's a rectangular extrusion,
6. Door Panel. The original is flat (no pockets, or speakers for a stereo),
7. Steering Column. There are noticeable differences in steering columns, hubs and directional stalks on the the originals against the replicas.
8. Door thresholds. Depending on the manufacturer, the threshold will be different. VS puts grip tape on the threshold. The original is a rubber threshold held down by aluminum strips. VS, JPS and IM all have the widened thresholds, similar to the original, but the Beck is much narrower which gives more interior room. On the original, the threshold has chamfered edge, whereas the replicas are mostly squared off. Also the heater opening is located at this threshold on the original; on the replicas it's forward the doors in the footwells.
There is a piece of chrome trim where the leather door panel meets the painted surface at the top of the door (on the original). The trim is deleted on most replicas.
9. Foot wells. The originals have map pockets at these locations, and fancier stitching in the carpet.
10. Pedal assembly. The pedals on the original return into the firewall, whereas the replicas do not, well except for IM. IM builds out the firewall to conceal the pedal assembly (if I recall).
11. Flooring. The originals used a rubber floor, whereas all the replicas I've seen to date are carpeted.
12. Heater assembly. Some replicas have a similar heater knob to the originals, where the later chassis models have the heater lever at the center parking brake.
13. Tunnel. The tunnel is the originals is flatter than those found in the VS and JPS. Beck and IM are more closely able to replicate the tunnels
14. Frunk. The original speedsters have a non-carpeted frunk that houses the spare tire. The spare tire is seated in the nose. Beck has the tire in the correct location. VS and JPS due away with the tire in the nose.
I'm sure I left out 1,000 other quick visual differences between the two. Hopefully those much wiser than me can help complete this list or modify any inaccuracies I may have typed.
I have also included a number of interior shots of the original, IM, Beck and VS to assist in seeing the visual differences.
-Kevin