Selecting a front bar is dependent on many other factors when trying to tune a road or track car
e.g.
driver preference
nature of roads or track you drive on and how hard you drive
tyres (size, profile and rubber compound)
front and rear spring rates and damper rates
rear bar or not and what size
presence of original rear rubber springs
ride height settings
car weight
toe in front and rear and camber and caster
For a road going Elan its a lot simpler assuming the car is otherwise close to standard
i.e.
If you are using an other wise standard suspension and I mean truely standard which most are not but using modern radial tyres rather than the original 4.20 rock hard cross plys the suspension was originally design for then a 7/8th inch bar is desirable IMHO
Yes it will introduce a bit more under steer but that is desirable to control the tail happy nature of an Elan on modern radials
This understeer will be more pronounced especially in slow speed corners when you turn in quickly as in a typical US SCCA cone course in a car park.
Overall the car will handle better in most road situations.and I would recommend it.
However .........
Most Elans do not have a true standard suspension setup and this invalidates all I have said above. If you have played with your suspension or the DPO did without understanding what was the effect then fitting a 7/8th inch bar may make it better or worse.
You need to take an holistic view of suspension... you cant just change items independently as they all intereact
One day I will will write a book - Zen and the art of Elan suspension tuning
cheers
Rohan