I've wondered the same thing, both the Spitfire & Herald share similar components (I think there's a ratio difference but otherwise the same basic rack) and have much tighter turning radii, so why did he fit rack stops to reduce this ?
The Elan is similar in having lock stops fitted to reduce the steering lock and as John says, this is probably down to bodywork and soft suspension. If you were using a tighter lock at slow speed, for example when parking, then there's no great problem on the TC because under no load there's clearance between the top of the tyre and the front wheel arch. Even with my car being fractionally lowered I think I'd get away with it.
The problem with the Elan as standard, and I suspect the S1/S2 (and possibly TC) Europa is when you go full lock and get suspension travel, for example turning sharply onto a ramp, etc. Then you can hit the wheel arch on the Elan quite easily because there's a lot of travel, enough to catch the body if the wheel is on a very tight lock.
One thing I haven't bothered to check out but which may also be a contributing factor is the method of mounting the anti-roll bar. On the Spitfire it's mounted via a drop link to the front lower arm whereas ours goes onto the bottom of the damper. Perhaps this reduces clearance ? I don't know but it's another difference between the donor cars and the Lotus which might be important.
