I had a 2TG in a 35, now transpanted into my 25.
I did it for old school cool, and the fact that the rally 35 had an intimate meeting with a couple of large brown leafy things and I had a 160 fly hp motor sitting on the floor.
Great low down grunt, but fickle on tune and set-up.
4ag would be the direction I'd go. Cheap, easy and tons of spare.
Cosworth head on a pinto will be cubic dollars to do right, and more fickle than a 2TG.
18R is a boat anchor. Put it out of your mind.