We have all heard the "some late IA's came with 289" stories, it makes for an interesting rumor, but that's about it. Put it in context.. any MKIA with a 289 would also have had to had the 6 bolt bell housing as the 289's used by rootes were not the reare 64 1/2 5 bolt block, they were 6 bolts, and then in that case you would assume they would have put in the wide ratio toploader as well.
I have no doubt in period that people switched 289's into the cars, perhaps when brand new, maybe some dealers did the job too.. but it would never have come from the factory.
Randy, I have a lot of respect for what you post, but you also have a sense of humor, I wonder some times if you don't pull peoples legs a little and have a bit of fun? Did you also say your tiger lacked the black paint detailing on the body, no body colour in guards, MKII seats in the interior.. and 289 from new 9also is it a 5 or 6 bolt block that was installed?) Also, a 289 installed by the dealer at extra cost is a BIG difference than factory.. it's like the difference between factory options and period aftermarket parts.. yes amco made parts for the Sunbeam, dealer installed them, but they are not "correct" factory equipment.