My advice would be if possible take someone with you who has had an Escos or has a very good knowledge of them.They will know what to look for in terms of potential problems.Also for what it costs get a full HPI check done as others have suggested. Modifications on a Cosworth YB engine have to have been done by a specialist who has the expertise to do it properly. It is a pity that there is no paperwork available but if the seller knows who did the work it may be possible they will still have a record of what was done. As to its value it will be worth less because of the non standard interior and lack of history. See what the seller wants for it and form your own opinion of what YOU think its worth. Good Luck with it, hopefully you may grab a good car for a bargain price!!!