Hi tony,if the pin is located in the flywheel and you are seeing top edge of slot in line with lower threads,surprised it is running at all,that timing is a long way out,checked the history of your van and would say it has not had enough oil and filter changes which contaminates timing chain and tensioner,also spoke to someone with same misfire at low revs and has changed everything under the sun including the whole engine and the misfire is still there,so think it must have ECU issues but would try and get valve timing sorted out.It would help if you had power air tools to do the job but it is possible to do without,main thing would be to try and source camshaft timing tool which locates into that slot you are seeing.
wickham
June 2010