It's basically impossible to definitively identify a tomato if you've lost/never had its name. Even if you still have information about its source and history. However, it's possible to say which tomatoes are similar in appearance and/or taste.

There are many large pink beefsteaks out there. We'd need to see the flowers, what the seed locules look like, whether there is a core, etc. Some very large pink tomatoes that have been around for a while: Dester, Giant Belgium, Mortgage Lifter. That's just off the top of my head.

Maybe Carolyn will chime in. If anyone will know, she will.

Note that you'll never be able to definitively claim that your grandfather's tomatoes are a given variety and should never share seeds claiming it's a given variety. But you could do side by side growouts of different similar tomatoes and see which one comes closest if it's important to you to determine that.

After 35 years, though, it's likely that even if your grandfather started with a known, named variety, it has gone through some changes (occasional crosses, mutations, etc.), unless he has been bagging blossoms or isolating his plants with a barrier. So if nothing matches on all traits, it could well be a variety or strain unique to him. If it's stable and reproduces reliably true, maybe you should name it.

Looks like an awesome tomato to me.

Maybe one day people will record genomes of different varieties and testing and matching unknown plants will be feasible. Until then, it's almost impossible to be sure of a tomato's variety once its name is lost.

I feared that would be the answer, it makes sense that a precise conclusion cant be reached.

Exactly why I came here to see if anyone knew, I showed a picture to a friend and he was interested in knowing what variety it was, at this point I havent given him an answer.

Its been producing true consistently over the past 17 years that I can remember. If it doesnt match any other tomato I might name it .... sounds like a great idea :)

He's never bagged the blossoms unfortunately. I do think its possible that a few crosses have occurred that have produced sublte changes... I do know that his neighbour grows tomatoes about 40ft from his garden bed. (Suburban setting)

Its a great tomato! Great flavour, big enough to slice onto a hamburger... several hamburger hahaha, and its not too mushy!

I can definitely get some pictures of flowers and a cross section of the fruit next time I visit.

my guess is probably brandywine??

Pink brandywines are potato-leaved plants. Red brandywine is regular leaf, IIRC.

Thankfully I had some time to visit my grandfather again, managed to get some more pictures

sorry for the immature fruit.. there were no ripe ones :(

There are details that just don't come across well in photos, like how they grow and behave "in the field" so to speak, etc.

How is the taste? If it's sweet, I would guess Mortgage Lifter would be a good bet as a variety your grandfather could have started with. It is regular leaf, large and pink oblate with frequently ruffled shoulders and sometimes green shoulders when ripe, good producers, and has been a popular named variety sold commercially and traded for a long time.

Giant Belgium would be another strong possibility.

You might consider getting some seed for ML and GB and some seed from your grandfather, and doing a side by side growout to compare them. Could be interesting and fun, and the worst that could happen is you would have tons of good-tasting sweet large pink beefsteaks. What a sacrifice that would be.