well heres my weigh in.
For my 77 celica liftback i went 1uz for a few reasons:
only out weighs my 20r by about 50lbs. so the vehicles balance doesn't change
solid platform for any future mods and the 6 bolt mains make it super strong
makes more power then any other stock motor for the money
just a couple extra notes for you.
speedhut.com - makes a gps speedo in kmh and it fits in the stock housings with a little bit of dremel work. all my gauges are from them.
beams 6spd requires you to cut out the floor to fit it in the car and that will probably rule out stock center console.
there is a guy on 1stgencelica.com that makes a direct swap engine cradle for the 70-74 celica. has a few options for motor mounts and has rack mounts as well.
I do like the beams though and am planning to put one with the 6spd into my 72 Celica. i look at the motor as a modern version of the 18rg. its a dohc 2.0L that is rev happy and plenty of power for the Celica in stock form. also the ITBs on it will give it a similar sound to side drafts.
77 RA29 Celica 1UZ almost done again
72 Ra21 Celica project