Yes it can be done, but it's questionable how worthwhile it is, as a general rule, for cars this age.
LPG conversion requires the same hardened valve seats as a ULP conversion, which is not cheap and given that there aren't any grey heads around under 40 years old, you'd need to be really confident that it was a good one you were having done.
As the cost of petrol rises, the inflection point at which it makes economic sense to do this conversion drops, but you're still talking about many thousands of litres of fuel to reach that point. Do you intend doing those sorts of miles in your FE? Bear in mind also that the price of LPG is not a constant either, and could also rise, wiping out your expected savings.
There's a worthwhile read on this topic from
Money Magazine.
cheers
RET