Classic/Antique Car Repair: rear main seal, good luck jack, block chevrolet

Question
what is the cost to repair the main seal on 283 small block chevrolet

Answer
That's not a Modle A, I don't know what it will cost, or how to do it.  If you do it yourself, the parts are almost no cost.  It's all labor.
Find a good shop and have them do it.
Also, find a chevy car club and join it.  They will have all the answers and be happy to help you.
Sorry I can't be of much help.
Good luck.
jack