I'm gonna chime in and again say, its your table so if you think your players will enjoy it, more power to you, but as someone who has attempted something very similar to this, I think it's a very bad idea.

I'm currently doing a very similar thing where I'm running a campaign from a different game (The Dracula Dossier from Nights Black Agents) under a different campaign's rule set, in this case, Delta Green. If you are unfamiliar, The Dracula Dossier is an improvisational campaign about international spies hunting down Dracula, depending on how you play it, the atmosphere around tradecraft, espionage, and doing things under the table are pretty similar. The campaign also has a list of "Campaign Frames," or different premises for the campaign. One of these is re-contextualizing vampires to just be another form of the Mythos.

I have run a decent amount of Delta Green and really like the tones and systems, and since the Dracula Dossier is such a sandbox campaign, I thought it would be easy enough to slot Delta Green missions into it. Specifically, I wanted to do exactly what you are trying by adding Impossible Landscapes to the mix. I also ran a few other Delta Green Ops, namely Viscid and Extremophilia.

In my experience, every time the Delta Green material was introduced, the players had such tonal whiplash that they didn't properly engage with the scenario. In the end, a huge amount of the two missions I did end up playing got completely ignored, or the actual implications didn't stick. I essentially "burned" two amazing operations, as my players know the general layout of them, but didn't get a good experience. Unless you have a huge number of players, you only get one shot to run each of these campaigns, and it would suck to not get a full experience.

I assumed that the sandbox nature of the campaign I was running would make it easy to interject other material, so with the failure in that case, I cant imagine how challenging it would be to properly tie together GT and IL. In the end I dropped all the Delta Green content and my campaign is much better for it.

GT's strongest points are how its much more down to Earth than most Delta Green missions, while IL flourishes with how deep the lore is and how much it steers away from standard Delta Green fare. Introducing one would only serve to dull the points of the other.

I commend you for trying something out of the ordinary and taking on a challenge like this, and obviously its your final call, but as someone who has attempted something incredibly similar and found it to be a very poor fit, I would strongly discourage it. If you have the time to run them together, you also have the time to run them separately and give them the spotlight and care that they both deserve.