Ive already got some gsxr600 throttle bodies, but couldnt turn down a bargain and brought another larger set, think may be from a GSXR750 but not sure, they are 50mm tapering down to 42mm but a strange cable operated secondary butterfly system ive not seen before can anyone confirm?

They look like they are from a 2000, GSXR750Y, also regarded as the first of the "K" series.
Its a straight forward job to remove the secondary butterflies. They are only fitted for noise emissions

Yep, thats the GSX-R750Y and K1 set of throttle bodies, you're looking at the STV pulley.
Not just the pulley as a giveaway, but the bodies can't be separated - a feature on the Y series. Latter K1's and K2 versions have splitting bodies, look indentical to the 1000 K1-2, and in fact, are! You'll see 35F on the latter 750 and 40F on the 1000.
They're all superb units.

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Originally posted by motorcycle_mayhem
Yep, thats the GSX-R750Y and K1 set of throttle bodies, you're looking at the STV pulley.
Not just the pulley as a giveaway, but the bodies can't be separated - a feature on the Y series. Latter K1's and K2 versions have splitting bodies, look indentical to the 1000 K1-2, and in fact, are! You'll see 35F on the latter 750 and 40F on the 1000.
They're all superb units.

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Its not worth going to the bother of making them fit if you have a good set of 38mmbore ones that fit.The 600s will be plenty big enough and give better driveability.
Paul.
[as ive already respaced the 600's 38mm is it really worth it doing these 42mm 750's on a otherwise standard 130bhp 2 litre?

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Smaller ones will be great, unless your Pinto suddenly develops a wish to rev to 12K.