If you get a spitfire catalogue from Moss Europe
www.moss-europe.co.uk they show all the parts you can buy to rebuild the racks yourself - more or less everything is available except the Lotus length tie bars.
<a href='http://www.moss-europe.co.uk/MossUK/Pdfs/Spitfire/Spitfire%20MZCP405%2093-128.pdf' target='_blank'>http://www.moss-europe.co.uk/MossUK/Pdfs/S...05%2093-128.pdf</a>
(The rack is on page 130)
The only difference on the Lotus racks from the Herald/Spitfire one are the tie rod length/threaded portion and the rack limiting stops.
The tie rod is 7.59 inches (ball centre to thread end) on the Elan and 8.715 inches on the Herald/Spitfire but has already said they cannot usually be altered as the rolled threads mean the diameter where the Lotus needs the thread is already sized to about the thread minor diameter.
The rack limiting stops (you can usually reuse both) are sized as follows:
Pinion end: 27/32"id 1 1/16 "od 9/32 " long spacer welded to the locknut
Outer end: A spacer 27/32 " id 1 1/16 " od 1 3/4 " long
I've never heard of the Midget rack tie rods fitting though - have you got a definitive tie rod length and threaded portion (and part number?) to check against an original Lotus one?
Lotus themselves did some Elan replacement racks back in the late 80's early 90's that were of "sealed" construction based on (I think) the Austin/Rover Metro one.