It's can be done. Look in Modified Tech, Search for "BENDIX ABS". I've posted on some threads regarding doing the swap to a D44 and eliminating the ABS, plenty of others have too. Going to an 8.8 shouldn't be too different.
The 90/91 ABS system was first generation. It does not include a redundant conventional system - Loosing ABS boost means ALL boost is lost. Mine routinely went into ABS mode for no reason (despite $$$ in parts and repairs), the diagnostic computer throws false codes, parts are expensive and hard to find. A number of lawsuits claimed complete loss of brakes. In theory you can pull a fuse and prevent it from going into ABS mode BUT it will still rely on other components (and fuses) for boost.
To do it RIGHT, you will need to switch out all the ABS junk under the hood to a conventional braking system. A 95/96 XJ booster assembly makes a good choice.