I found this http://www.dixiemontecarlo.com/Product/Detail.aspx?s=DM90224&d=667&p=1 fuel sender for $138.00 shipped.

I had always heard that the angles were very different on the Elky vs the Monte Carlo. I think some guys have even tried the Monte sender with no success. Don't know if this is just an advertising goof, or maybe someone figured out something. I would vote for the goof. Make sure they offer a no return hassle if it doesn't work...

That's the sender I used for my LT1 conversion. I got lucky and scored a sender from a local wrecking yard. I don't recall any issues with the fit. The only issue is that the fuel gage reads nearly empty when the tank is almost half full (that's a 22 gal tank in the El Camino) I put on a fuel pump for a TPI Camaro in place of the TBI Monte Carlo pump -- fits perfectly and gives the pressure you need for the LT1 fuel injection.

the sender for the monte is wrong for the elco.monte tanks only came 18 gal.you can bend it into shape to make it function but wont be accurate.you can use the efi tank and carb sender with a external pump and it will work fine.you can do as i am doing with my 86 ss lt1 swap. i am useing the tank from a 94/96 caprice/roadmaster wagon 25 gallons,corect pump for lt1/tpi,almost a drop in and dirt cheap.the straps are in the correct place,you just need to make a bracket to hold the fill tube to the fuel door well.thanks for the link to the monte sender as i have both cars and am efi converting both.its getting too hard to find a decent carb core any more.