I'm looking at my AES-10B and it looks like it has the 2 fangs for the type 1 bayonet on the FSB. The bipod is in the way, so I can't confirm it by putting a bayonet on. I kind of want to swap it out for my MAK FSB, but then there is no hood on the front sight.
Those little "fangs" can be found on all RPK's and also serves to secure the end of the cleaning rod.
Removing the FSB from the RPK for a MAK-90 and using the MAK-90's FSB to replace it would probably be a very wasted effort. You'll just wind up having two rifles with incorrect FSB's and a great deal of time wasted.
But I want a type 1 bayonet lug.
I think cannabalizing your RPK for one probably wouldn't be the way to go. Especially since you'll have a hard time find another for it to replace.
There's a Bulgarian front sight base like the one you want here:
And here's an actual Chinese one:
This ^ is your best bet. The RPK FSB is considerably larger in ID and would need to be shimmed to fit. The Bulgy fits the MAK90.