Something else you have to recognize is that even a fullyrenovated and updated (not restored) old home is loaded with functional obsolescence, and to use new, contemporary floor plan homes as comparables
could be a BIG mistake. Generally speaking, I like to use at least six comps on a home like this. Throw in some older similar homes if possible (even if they are old sales, use time adjustments, if indicated). Throw in some older, dis-similar style homes. Throw in some newer homes in similar locations and/or sites. Try a listing or two. You should expext a larger than typical range of value when done. Explain this in your scope, and reconciole towards the most comparable "comps" you have.
Also, I have found that this statement works WONDERS in this type of appraisal:
Per FNMA Underwriting Guidelines, Section 408.02, "Occasionally, there may be no similar or truly comparable sales for a particular property-because of the uniqueness of the property or other conditions." Per FNMA's recommendation, the appraiser has used his "...knowledge and judgement to select comparable sales that make the best indicators of value for the subject property, and to make adjustments to reflect the actions of typical purchasers in that market." The sales presented were judged by the appraiser to be the most comparable found. The appraiser has expanded the comparable search parameters, and has exceeded standard FNMA guidelines, and adjusted for significant differences, per FNMA's recommendation.
Except for VERY few cases, there is little "historic" value in older homes. If you feel youes is one of those, than as Karl suggested, get some help from someone who has experience in this...
Also, as Greg states, you will find the sales, you just have to look hard. I just completed a 1923 home in Melbourne, (actually the historic districe of old Eau Gallie), over here in Brevard County, and found 5 sales in comparable neighborhoods built from 1882 to 1935. None were comparable, really, and all were dis-similar in design, but that is what I had to work with. I'm sure you will find some...