its really difficult as its clearly not a s1 shell,but the car now has gained s1 i.d. from somewhere
personally i think it would have been better if it had been a xr3i/rs1600 id with all s1 bits fitted.then it can be sold as a genuine replica.

its very sticky ground-i would break it

but to be fair i bet even the dvla examiners dont know about the early/later strut top issue,but they will know about floor numbers being changed/erased.unless its had the floorpan welded in from the s1.......
glad im not selling it

maybe the mods should look at this and advise the seller accordingly