Doonside Mills, two series both serial numbered 100. The engine with the aluminium head is a Series 1 engine. There were only 100 engines in this series and this is number 100. This engine is mint and unrun. The engine with the green anodised head Is Series 2. This was much longer production run (over 1000 ???) and this engine is also numbered 100. The engine has been bench run but is in excellent condition. Both engines come with their very plain original cardboard boxes and instructions. These were originally written on a typewriter and reproduced on foolscap paper. Written by Ivor F in SR1 (Spelling Reform 1) in which words are written phonetically so that ‘head’ becomes ‘hed’. The strangest instructions you’ll ever read. The engines were produced by Ivor F and Gordon Burford. The engines will be sold as a pair and will not be separated.