The problem with doing this mod on an early small log head is that you are starting off with a smaller intake bore and then have less metal to play with.
On a flat-topped log it will look something like this when you are done. This is a picture from our book.
Look carefully at the end of the adapter. You'll see that the manifold is milled flat. The orginal 1 3/4" intake bore is enlarged to an oval shape. I leave the orginal carb bolt holes to use for attaching the aluminum plate. You need about 1/8" of material to seat the alum. adapter plate.
The 1/2" alum. plate (that you have to make) has a slight taper to its ends to match the carb bore to the newly ovaled manifold.
If you look carefully in the background you'll see a Hex log head. It had to be welded up to get enough meat to seat the alum. plate. You could do something like that, but the additional welding and machining will cost more.
You could also make an aluminum plate adapter to put a Holley/Weber 5200 (it's like 1/2 of a four-barrel carb)on your manifold. You'd make it from a one inch thick plate. This sketch is for the larger 1 3/4" opening log, but a couple of guys here have the drawings for an adapter to the 1 1/2" opening that you have. You'd probably want to bore out the 1 1/2" hole to ??? something bigger. Do a search. Three of us discussed this at length.
The plate's log bore is offset to the two carb bores on purpose. It is so the carb will clear the head.
Good Luck