I wont lie, I frequent honda forums allot and they're latest contibution (beside homedepot garden trim lip) is to use motorcycle itb's on their motors. The really ghetto ones they make, they just cut up their stock intake at the runners and fit on the throttle bodies, weld up some support, and use the stock location injectors. The people with fab equipment buy a flange, have the runners straight and evenly and space out. They then machine the itb's injector location to fit theyre original injectors for better mixture of the fuel and air.
After looking at the stock intake manifold on a l28 it doesnt look like the ghetto option will work because the outter runners are to close together for the itbs.(yes you would have to buy 2 sets and cut them up)
So I'm guessing you'd have to cut it after the injector hole and weld on the appropriate sized tubing and weld it on at angles to get the itbs to fit on properly. I dunno, was just tossing around some ideas. Trying to keep efi(megasquirt) with a na motor but know that the stock intake manifold is basically 6 straws connected to a lawmower's throttle body. Looking for a solution that is about 400-600 with somewhat minimum fabrication as ill have to get it welded somewhere else.
Here are some examples of diy itbs.
Here you can see the chrome spacers used to evenly space out the throttle bodies.
Here are some on a m20(?) 325i engine
And finally someone that angled the runners instead of spacing out the injectors.