Among the top 3 makers (Vintage, JPS, Intermeccanica), it's fairly easy to determine the manufacturer just by a few visual cues, if the person selling the car doesn't know who built it.
Vintage & Intermeccanica put the speedometer on the left (ala T-1s); JPS puts it on the right (like post '57 T-2s).
On VS cars the dash leather does not touch the leather on the top of the doors - there is a noticable gap at the windshield posts. On JPS and INT cars the dash and door materials touch - no gap.
On the rim of the engine opening JPS and INT use four round rubber discs to cushion the engine lid. VS uses a full gasket around the entire opening.
There are many others, but that should get you started. Remember all replicas are custom made so this info should be thought of as "generally true" not absolutely true for every single car...and it's probably truer for "turnkey" cars than owner-built kits.
If you can take a few pics and post 'em, ID-ing the maker should be easy.
(Message Edited 11/9/2002 11:40:54 AM)