I don't know what size the dimensions are, but the later S10s, full size trucks and LS1 ('98+) F-Bodies used a hydraulic bearing that may be a cheap alternative.
http://www.autozone.com/autozone/parts/1998-GMC-C1500-1-2ton-P-U-2WD/Clutch-Slave-Cylinder/_/N-ja9ljZ6o2ja?filterByKeyWord=slave&fromString=search
I did a little searching and a late model GTO also has a hydraulic throwout.
http://www.autozone.com/autozone/parts/Duralast-Clutch-Slave-Cylinder/2004-Pontiac-GTO/_/N-jli85Z6o2ja?itemIdentifier=252779_204487_0_