Hello and Welcome to our Forum from Florida! We are glad to have you join us.
As for your 75B and the holster, I really can't help you with that. I did however want to let you know someone saw your question and welcomed you as a new member. I have a 75B Omega but I don't have a Forbus holster and haven't in quite some time. I thought the only thing that changed was the trigger system, not the trigger guard also. I'll dig mine out and compare it to one of my original 75B's and see if there is any difference.
I do have a suggestion though. If both the pistol and the holster are Brand new then you can start off with wrapping your pistol with wax paper (mostly just the part that fits inside the holster) and let it sit in a window or sunlight for about 2 to 3 days then take the pistol out, remove the wax paper and then try putting the pistol in and drawing it. Remember to use an Unloaded weapon (that's the legalese part, just to be safe) for this process. It may draw easier than it did. You will all so have to wear the holster and the pistol (unloaded) together for a few days. It's all part of the "Breaking In Period" most everyone has to go through with brand new Leather holsters. (actually you didn't say if it was all leather or a hybrid or all Kydex, I just took a while guess
). Pretty much like breaking in a new pair of leather shoes Especially boots.