That'll only work on the 1300 - it does work well on that engine.
There is much less choice on the 1147 as pistons 2 and 3 have joined inlet ports. There are manifolds for side draught carbs (SU or Stromberg) and that's what the Triumph people use but on Amphicar the muffler is in the way so you would need to make some sort of 90 degree elbow to fit a Weber.
There is a small Weber that sits directly on the standard Amphicar manifold, might be a 32ICH ? I've seen it on Triumph Heralds of the era but never on an Amphicar.
In the 1960s the UK Amphicar main dealer had a tuning kit made for the original engine with a tubular manifiold and Weber carb, picture here
It's really well made and was used on their demo car. I'm not sure if it was a one-off but I've never seen another. It joins the the standard Amphicar muffler. It's in my garage and originally I was going to fit it to my Amphicar but went the 1300 route instead.
Here is a photo (3rd to last)of the side draft webber on Finzilla. I have added the exhaust , out the opposite side.I also modified the stock exhaust/intake manifold. Runs SWEET!! E mail for photo. Tom [Meet Finzilla!!
Yes , please send me your photo on the exhaust. I am having a guy (have
been waiting for 6 months, now, to make a header flange and have a guy
lined up to make the tubing to make a header to use with mutiple carb
set up. I would love to see what you are up to. Thanks, Amphi-