What is this 1983 XJS-C that's not a real factory one?

It’s for sale in Norway and the seller claims it’s not an XJS-C, but something rare and unusual. The seller says “possibly a prototype”…

The VIN is sajjnaew3bc110500, which decodes to a 1983 XJS V12 Coupe.

I’m assuming this may be a third party cabriolet conversion? I recall Banham and Lynx doing them, maybe others.

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I think something similar was discussed in this thread from last year.

It’s a shame that thread went no further. Would have been useful to see some photos. I suspect that prototypes would have been earlier though, given that the XJS-C was put out as a 1983 MY?

Agreed. But there are a few folks here who own XJS-C and are very knowledgeable, hopeful they will chime in.

I am no expert, but if the VIN decoder says coupe, then it is most likely a custom conversion.

According to the best information I have, there were 206 XJS-C’s made in 1984. 5 in 1982, and 163 in 1983 .Hardly a prototype then. The photo below is of my 1988 “real” XJS-C. Look at the “B” pillar and the shape of the rear side window. Rounded, not angular.
The roof on the “prototype” has hold-down clamps for the top directly above the sun visors. Mine are above the rear-view mirror. Too bad there is no picture of the area below the IRS cage. There should be some reinforcement there, easy to identify. I agree with Steve- a conversion.

Those are not 1983 wheels.

I have no useful information to add, but I saw a very similar car for sale in the USA a few weeks back on craigslist maybe? Can’t remember but it had the same exact weird convertible / cabriolet thing going on