D and L Transmission seems to stock a good supply of Muncie parts had prices that are less than what you’ve got so you may want to shop around a bit and just call these guys. 1-631-351-4837

http://www.dandltransmission.com/muncie.html

Specifically:
Gear, cluster (counter), Muncie 1" M-20 wide 25-22-19-17 made in Italy $192.00
Gear, cluster (counter), Muncie 1" M-20 wide 25-22-19-17 excellent quality, made in Asia $148.00

Gear, input (main drive), Muncie wide 21T 10 spline (66-70) $152.50
Gear, input (main drive), Muncie wide 21T 10 spline (66-70) made in Asia $118.00

It may be that the prices you have are for OEM US made components. There are some pretty good deals on the Italian and Asian replacements and if after talking to these guys you feel like they’ll stand behind the import parts, they’ll probably hold up just fine behind your 283 in the '57.

TB Transmission also has a good web site and a good selection of parts. 800-425-4226

http://www.tbtrans.com/muncie_4_speed.htm

I have not done business with either of these firms, perhaps others will chime in.

A quality rebuilt M-20 is worth, in my opinion, $1,000 – 1,200. Good used will set you back $750. A Super T-10 replacement from Richmond Gear is over $1,500 so you need to decide if rebuilding your $50.00 find is worth it – I’d go for it – if for no other reason than it’s keeping a piece of hot rod history intact and will give you a great sense of pride when you finish!

Bear in mind that this is complex process and the first time is very time consuming. Get a book that shows detailed illustrated parts breakdowns of each step and take your time. Make sure all your pieces are really clean and use lots of lint free rags and wipe everything off (especially your hands) to make sure you have nice clean, good surfaces to hold as you assemble. If you have a well ventilated are to work in, Acetone is a good solvent for this type of work. A book will also give you some tips in reference to order of assembly that are critical for a proper rebuild. Everything should be butter smooth when your done and the assemblies have to spin without any “rough spots”.

Let us know what you decide and take some pictures for us to enjoy your progress. Have fun with this!

Regards,
Glenn