they do say you can get a spacer instead of a new manifold.
Yeah, they're full of BS. You can't put a four barrel TB on a two barrel manifold with an adapter and expect it to perform. Edelbrock makes a dual plane intake that has the correct angle for the four center bolts but here's another problem you're gonna have, the swirl port TBI heads suck or actually I should say they won't suck air. I learned this the hard way on a 79 Malibu I used to have. V6 blew up, dropped in a 355 bottom that I had saved and scrounged a set of 1.94 TBI heads for it and used the Edelbrock dual plane spreadbore manifold for those heads. It ran great!,,,,,,,,,,,,till 4400 RPMS then it was like pushing a wall. I wound up having to pull the heads back off and grinding all that swirly ramp out and opening the ports up under the seats and then they were only a little better, I could get it to pull up to 5000 before it hit the wall again.
If you're gonna run that four barrel TB you will need to get better heads and cam or there's no use.