Here is a great link I found I believe years ago in Hemmings but they make tranmission adapters for almost any engine to any tranny and they have MEL 430 listed to adapt to a small block Ford tranny or a Chevy. If you can handle the mods for a crossmember or whatever else you might need..might work out great for your C-4 issues. They are not strong enough like mentioned in the previous post. I have a C-6 and the guy who built it for me told me I did not need a shift kit..he just adjusted the valved or something and it shifts hard like it has a shift kit. Have not been able to try it yet since its only been driven 3 miles in the 9 years I owned it, but a C-6 should do the trick just look out for mounting mods that might need to take place. I am sure someone out there has done this so keep looking and try the Lincolforum.com. Take care
Here is that link..copy and paste it or just type in the main address and you will find it. Good luck and let us know sometime what happens!
http://www.transmissionadapters.com/Lincoln_Edsel_Merc.htm