898 kilos, Mark, you just wrecked my weekend with this feature!
I dont remember the weight scale for the Grp 1,5, but a MkIII appendix should be around 1061 kg, impossible to achieve if you start with a road going car and keep its metal panels (my MkII is around 1073 and could be 1051). Had a look to the auctioneer's site but they didn't show the suspension or brakes details. What a nice car you got !