I'm the guy who has the 1st engine in the 3TJ frame. I have moaned a lot about my bike in the past but I love it!! Someone went to a lot of trouble to make the heavy brackets for the front mounts. It has to have 3tj inlets and carbs otherwise it would be too tall for the tank.
Very little vibes and the fixings seem to be ok. The only fly in the ointment is the engine has loads of 3tj parts making it hard regarding spares!

Would I race it? No just love riding it and waiting for a fuel pump unfortunately but now I've done a few more jobs it's getting better!

I guess if they made mine fit you could make yours fit, but if I had to do it again I would get an engine that fitted straight in so I agree with other posters get the engine that will quite happily, and not one you have to make brackets for.

HTH but I love a chance to say how much I like mine!!