1966 Plymouth Valiant 273 rubber engine mounts

Whatever you do, don't try to use the ones currently listed by most suppliers (commonly a 2266)- these are actually later mounts, and not thick enough for the early As; using them can cause fitment issues like exhaust or centerlink interference. The actual number is a 2338, but is out of stock at most places.
The common work-around is to use a 2469 or 2710 Dodge truck insulator, which are the correct thickness and have other advantages too. Particulars are here:
JimBowenTheHolyGrailofMotorMounts.pdf (earlycuda.org)
The good news is they're only 5-10 bucks a piece brand new.