Yes cylinder heads and most of the parts will interchange, if they are NON "Power Improved" style heads. Your '91 Towncar uses an aluminum intake, while Mustang intakes, and other Ford cars of post-'96 model year, use plastic intakes. The engine block however, will NOT interchange. This is because the '91 to early '92 model year 4.6L blocks used the same six-bolt bellhousing bolt patterns as the 3.8/4.2L V6 and 302/351W V8 engines. Mid '92 model years changed to the seven bolt style bolt patterns with the introduction of the AOD-E transmissions, utilizing the three bolt starters that every Ford technician hates having to remove. Hope this helps.