Can I put a kit on the 735 bmw to look like the new 740's and still look authentic

I have seen it done for a special training center of BMW in Germany.

It would be too much money and work to do it for the average consumer though.

no you cant the wheel base is completely different your car is e32 and the 1995-2001 is e38

There are 735i s, 735iL, 740i, and 740iL with V-8 or V-12 engines. You might do a whole lot of work modifying one car to look like another, but at what expense? Unless you have access to salvage 7 Series BMWs, the cost of your project sounds so expensive, it could never be worth your time or mental anguish to even attempt.