Eric - "All things being equal" is always the big question.
I can't do that on these 2 cars for you, but you or whomever does the PPI for you should use Jeff Bowlsby's condition assessment form at the link below to evaluate that "equal" -
http://bowlsby.net/914/Classic/zTN_Gen_914CAF.pdfAlso - in addition to the 914 Info section at the top of this page, Jeff's & Steve's 914 sites are good info for 914s -
http://bowlsby.net/914/Classic/ p914.com (& .org & .net)
Also - do you prefer the late 75-76 big bumper 914s, or the early 70-72 no-tits, or 73-74 tit chrome/steel bumper 914s looks?
As for the two 2.0 motors - the 73-74 GA code 2.0's are 91/95 HP (SAE/DIN), while the late 75-76 49 state GC code 2.0s drop to 84/88 HP (SAE/DIN), & the California GCs with the crapalytic converter & different detuning for smog were only something like 80/84 HP IIRC - which is comparable to the 70-72 1.7s (49 state 73 was 80 DIN, but the Cal 73 dropped to 69 HP).
Also, the total curb wt. is 100-200 lbs. more on the big bumpered 75-76 914s, so the power-to-wt. ratios are also lower. I test drove some new 75 & 76 2.0s when I was deciding on my 73 2.0 during late 1975, & I could tell a definite difference, & felt that it was almost like my buddy's 71 1.7 (which he still owns w/ 71K +/- miles).
So there is a definite power & performance difference, but those bumpers will give you more "bump' protection (5-7 mph range).
There are also a lot of other trim, fitment & materials differences in the MYs, so look at p914.com for the range of those changes (e.g.: in 74> the turn signal indicators went from L & R lights to just one for L&R, along with black button gauges with plastic bezels from glass, tartan fabric inserts became available 75>, etc., among other changes).
And be aware that as of today the 1976 2.0s still have to pass bi-annual smog tests in CA (no 1.8s made for 76 MY), so they're hard to sell here.
All things NOT being equal - at this point pick the best condition, best sorted one you can find - or the best project basis one, if you're looking to work on one.
PS - The 73-74's tend to have better values & appreciation for the above reasons, & probably will continue to, & the earlier 73s all/most had the Appearance & Performance Groups of options included on them in the base price up to +/- March 73 production/sales - so it's easier to find a "loaded" 73 2.0 - but there are/were fully loaded 74 2.0s too, but you get the rear bumper tits & the other MY changes.
Happy Hunting!
Tom
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