I think the 91 mustang engine had a fuel pump cam in it, but not sure...I used an electronic fuel pump on mine because the 87 Ranger FI block didn't have the hole cut for the pump...worst case scenario is that there is no cam and you have to plug the hole...best case is, of course, you can use the manual pump...
But if you go with the electronic pump be sure to get a low pressure that is rated 4 - 7 PSI only or you will have, ahem, issues...and even then you may find you need to adjust the carb float a bit because the pump may be just enough to squeeze past the needle in the carb...
The good news is that adjusting the carb float is fairly simple...the not so good news is that it takes a bit of patience and care to put it back together...
Otherwise, I used a 2.0 intake on a 2.3 head for about a year...the only problem I had was with the carb float...it was about the same on gas and power...maybe a bit more since the 2.3 block I put in had a bit more punch...oh, and the emissions on the 2.0 are a RFPITA...that's why I went with an 87 Mustang II carb and intake (motorcraft 5200 carb on Offenhauser type intake)...Fuch mucking etterbay...