mustang gauge proble

I have an 83 drop top I bought new, it has only 3800 miles on. It had no balls so I never drove it , few years ago I built a roller block 302, and swapped out the original 3.8. I used most of the original wires and all original sending units for a 302, I have the original dash electric gauges(don't work) and some summit gauges on the cowl (these work) My problem is that I want my original gauges working especially my gas the gauge, So I have new sending units and have used the original wires, (except for the v6 wires) but they don't work ! any Ideas what I may have done wrong ? thanks john jkimball@twcny.rr.com

yes 3800 miles

like I said I bought it new and because it had no balls. it didn't get driven, then one day I decided to fix that issue by putting the v8 in it. I've had to do it on a budget by myself, so it has taken many years, the only changes Besides the engine, was the rims and tires ,and a new top last weekend , The top craked from sitting in the garage, as far as pics ,I'll take some, but if you know what they looked like new inside and out ,,thats my girl. she sitts next to my 65 drop top that I bought when I was 16.