I don't think 91' LTD's (Crown Vic) came with C4's. I could be wrong but I'd say it's most likely a 4spd Overdrive transmission in there not a C4.....Probably an AOD-E. Might want to check that out a bit further. The guy's above are correct, that engine is going to be dead horse. Crappy Head's, Crappy Cam, Crappy Compression etc etc. You Get The Point. I don't mean to discourage you at all but if I were you I woudn't waste your time with that non H.O. 302 It's not hard to find a decent used 5.0HO and trans. these day's. Take your time and when the right deal pop's up snag it. You will have more power and your option's won't be as limited with the H.O. In the long run you'll save money, cause if you buy that Non HO, before you know it you'll be converting it to roller, buying E7's etc. etc. Buy an HO and you already have all of that. Do it right the first time man.