There are some pictures on Steve Gray's website...
http://www.stsa.co.uk/gallery/5EXi/B...-SteeringRack/
...looks like he had to add some tie rod extenders?
Early Marlin articles certainly mention they use a Metro rack.
A quick call to:
X L Steering Division
01384 405900
7-8 Gibbons Industrial Park, ,
KINGSWINFORD,
DY6 8XF
might tell you what type Steve's is?