Did you get your motor through Southern Automotive? They use 20W50 weight
oil. It’s pretty clingy and as long as you didn't run it too long, I doubt any damage was done. The
oil filter listed in Unique's build manual (or at least when I built mine) was a small Puralator filter. They list it because if you are not using a remote filter, that’s the only filter that will clear the frame. I would recomend using Ford Racing's FL1-HP (I think that’s the correct part #). I bought mine through the local Ford dealer. You can see a pic of my filter set up on one of the Dick Flesher's posts
Will exhaust pipe work as a radiator hose? . Having the lines hooked up wrong may have damaged the inner seals of the
oil filter. Oil will still flow but may not completely filter all of the oil correctly (i.e. not damage anything in the short term but by not properly filtering could cause damage in the long run). Therefore I would recommend replacing the filter now. You might also consider replacing the oil now if you think its viscosity might have been compromised from the short term of improper oil flow.