Its a little backwards from your thinking...
The old intakes are 90 degree bolts. The deck surface is only about 1/4" thick. If you were to mill the holes for a 72 degree face, you wouldn't have any thickness left. Instead, the common alteration is to use a tapered washer over a hogged-out hole.
But, you may or may not need it. Starting in 87, TBI engines got the funky center bolts on the intake. TPI kept the standard small block layout. Starting in 96 was the Vortec pattern which was eight 45 degree bolts instead of the twelve 90 degree bolts. That one you can't really alter since the ports are taller as well.
Edelbrock makes plenty of TBI intakes with the 72 degree center bolts, as do a few other companies. For the sake of mocking up an engine, all of the intakes (of the same variety) are basically the same except vortecs. Vortec intakes are taller. So, if you want to mock up the engine, you can assume that pre-87 intakes are the same exact critter as 87-96 intakes, they're just cast with different center holes. For instance, a Performer RPM for a pre-87 engine would be the same height as a Performer RPM for an 87-96 engine.
Edelbrock has a section of their website devoted to intake measurements. You can compare the intakes first for yourself.