The Corvette Central one should work, as it is designed to go in series with the sender. The other Wilcox one is designed for a different, older type of gauge and hooks up in parallel at the back of the gauge. I don't think it will work in an H-body.
That being said, a fine adjustment potentiometer is nowhere near $30; any electronics supply store should have one for under $5.http://www.digikey.ca/product-detail/en ... ND/1087574
77 Vega Estate wagon- project(someday)will have TPI305/T-5, S-10 spindles/axles
72 Vega HB Drag Car -383/'Glide/9"(firstname.lastname@example.org)(email@example.com 1/8th)
76 Vega GT- 400/4spd/9" retired from active duty(rusty)
03 Silverado 2WD ex.cab (work truck/parts hauler)
04 Silverado 2WD ex.cab (retired)
06 Haulin' 20ft enclosed car transporter
93 Suburban- 350/4L60(retired)
00 Saturn SW2- wife's car
01 Saturn SC2- younger son's project
00 Saturn SL2- daughter's car
98 Saturn SW2- spare
and 3 more Saturn "parts cars"
Note- the very act of listing all of these has made me realize I have some kind of problem.....