Modify it how?
It's a pretty standard pump, being a Metric Saginaw case. I've seen it in quite a few late-model GM cars and trucks, some Dodge (even the Viper!) and maybe a few other applications - but I've not compared the mountings. I do know that the Viper takes the same cap (much to the Viper owner's surprised and my pleasure, when he let me horse the thing around for a bit. Nice ride, but it would cost me WAY too much in tickets to own one!)
I don't see why, say, and F-body pump would not fit - but if you want to improve steering, you might want to think about changing the gearbox rather than changing the pump. The gearbox is where the magic happens - the pump is just a pressure source. Something to consider (and, as I recall, the gearbox is a 3-bolt Metric Saginaw case, which can also be replaced with some 4-bolt cases as well...)
5-90