Hello George.
As someone who owns a 77 Archer the subject of wheel spats is one close to my heart as the pre 78 models had smaller spats and not the 'pants' common to most peoples impression of the aircraft. The difference is that the earlier ones are worth 3-4 knots and the full leg pants around 7-8.
If you would like me to forward the relevant performance graph from my POH I would be happy to do so. PM me an email address and I'll mail it over.