Aircraft Inport Question????

Need Some Advice From thoughs Who Know,

Say you found a 1984 172RG that has had a 250HP powerplant put in and some
extra long range fuel tanks but no STC's or any other paperwork for the
aircraft except for engine airframe and prop log's. Aircraft also has some
very odd instruments also that would have to be replaced with standard
measurement instruments. Do you think it would be a problem bringing this
aircraft in to the U.S. If the price was right? What hoops would one have to
go through or should one pass because of a night mare of paperwork.It is
legal to fly in country of origin!