Making the 74 in same condition as the much better looking 75 will cost much more than the price difference. But if you will cut it down with tiger saw and create something else than Honda did back in the days, the 74 might be OK too.
How it look on the outside can reveal how the bike has been taken care of during the years, the inside (not visible) might have suffered as well.
It depends what you want, making them look good $4000-6000US is easy spent in parts. You do most of the work.
If you want to restore to almost OEM look, calculate with some $$$ in parts only. Cut valve seats must be left to professional when the tool is expensive.
Restore engine $1000US will be spent rather quick. Gasket- seal kit, clutch, all internal chains with tensioners, maybe cank bearings, bore with pistons will add cost. Head refurbish- cut valve seats etc etc. Cam holders can be bad due to lack of oil to cam bearings.
New 4-4 exhaust $3000US with all small details needed. (If 4-4 is important, better to find bike with them on)
New paint with trims $1000US (500 if you can do the spray job in the garage?) (new tank + sidecovers from Yamiya $2000US)
Fix frame - sand blast + 2k paint or powder coat, $150-300US ?
A few hundreds in difference might end up in addional thousands when restore...
If you start to restore, you might have an idea from the beginning. It's a huge risk that you see all dirty and bad details and change more and more to new after market or NOS. - How do I know that??
I'm now at least $5000US over my initial budget I had in mind 2011-2012 despite I knew what might happen since I repaired and upgraded the entire bike 30 years ago for money enough for a new Kawasaki 1000J. I'm happy that I kept my CB750.
Now having thoughts about another $2000 in new carbs....

Its probably cheaper to find a restored complete bike for $5000-6000US than buy a forgotten not complete half rotten barn find for $500-600US and restore it.
Anyway, its fun, no regrets except not buying CB750 parts and additional bike 10-20 years ago while my bike was sleeping in a friends barn and all these stuff still was cheap.