This is how they left the factory..haha! Just kidding, I've had three Marinas, thought they were much maligned. Great run-around classic. I'll be interested to see how you get on. I drove a Marina Coupe, ERW 875T at Drive Dad's Car, first time driving one in 30+ years, impressed that particular one drives really well. Started first time, unlike the Rolls Royce, which had to coaxed into life, there however, all similarities ended.
You were there, you had it running, why didn't you try engaging a gear to A: test the clutch B: See if you had gears C: make sure the brakes weren't locked ?
I wanted to but the second time I tried (starts and cuts out) I'd run out of battery ☹️. It does go into gear and the brakes seem to have some effect when I have tried it.