You should have gone for a new head instead of welding, I did the same mistake. Are you sure you need a overhaul because the symptoms you are telling might be due to a blown head gasket or welded head being cracked. For effectively knowing if it requires an overhaul you must get a compression test done but I am not sure if it can take place with a gasket or head failure. Did you put in a genuine gasket and not those paper ones. For mechanics please contact noomanghori a PW member on the following thread post#93 he says he has good mechanics contacts:
Also on the same thread a PW lowresolution post#122 may also be able to help you.
If you want to see kabli engines and get an estimate contact imran manan at gharibabad 0321-8221732, 0347-2000300. But he has only EFI engines. He may be able to arrange a carburetor one but you won't have many options to find a clean piece. There is a whole market in gharibabad of kabli engines but he is the most reputed one.
For overhaul always remember as Xulfiqar bhai says you need proper tools. Rest the experts will help you decide.