I got a 88 750il that needs a new front bumper. Does the 735 bumper fit it. I looked on realoem and there different part#s. But the guy i bought the car from says he put a 735 rear bumper on the car. So I wonder if they are interchangeable.

Bumper itself fits, just the lower lip is different and the air hole on the driver side is not there for cooling.
If you buy a bumper from a later model 750 or from a 740, you will have the larger spoiler lip with 2 inlet holes for front brake cooling.
The lower parts are also availavle as extra parts and can be added.

Ask here if someone has a front bumper for a 750
http://www.bimmerboard.com/forums/e32/
But basically it fits, the only differences are the lower lips and air inlets.

newer facelift version 750 with deeper spoiler lip and 2 air inlets
http://img.villagephotos.com/p/2004-6/738636/iL%20(01).jpg
and that is the one from the 730/735
http://cgi.ebay.de/BMW-730i-E32-KLIMA_W0QQitemZ230065131512QQihZ013QQcategoryZ9801 QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
730/735
http://cgi.ebay.de/BMW-E32-TueV-Au-2008-Sehr-Schoen_W0QQitemZ130061685681QQihZ003QQcategoryZ980 1QQssPageNameZWDVWQQrdZ1QQcmdZViewItem

thankyou sir, your knowledge is immense. I think I will have many more questions about this car. This car is so much different than my 535. To me it looks like a whole new project that I can't wait to restore to its old glory.

Welcome,
if you want to specialize on E32, here are the specialists all together including myself
http://www.bimmerboard.com/forums/e32/page/0

I can't wait to restore to its old glory

Just do it, we can help you, no problem.
I have done that too. And I have at the moment a 750iL Highline under restauration, and have some more E32.

thats good to know, because this car has many problems. But thats how I like them.