  Differential cross sections for the electro-disintegration process $e +
{^4He} \longrightarrow {^3H}+ p + e'$ are calculated, using a model in which
the final state interaction is included by means of a nucleon-nucleus (3+1)
potential constructed via Marchenko inversion. The required bound-state wave
functions are calculated within the integrodifferential equation approach
(IDEA). In our model the important condition that the initial bound state and
the final scattering state are orthogonal is fulfilled. The sensitivity of the
cross section to the input $p{^3H}$ interaction in certain kinematical regions
is investigated. The approach adopted could be useful in reactions involving
few cluster systems where effective interactions are not well known and exact
methods are presently unavailable. Although, our Plane-Wave Impulse
Approximation results exhibit, similarly to other calculations, a dip in the
five-fold differential cross-section around a missing momentum of $\sim 450
MeV/c$, it is argued that this is an artifact of the omission of re-scattering
four-nucleon processes.
