Like any job I do for others, or myself, you have to ask ... "What's your budget?" This is the one question that when I am building/rebuilding, I almost always go over budget. Cost is so fluid a concept, "Where do you live, cost of machine shops services, Parts costs, etc" all vary quite a bit due to geographical areas.
Your 4.0 is a OHV (guessed from yr) As far as I have read, are not prone to head gasket failure, Like the 90's 3.8's. So just doing a head gasket job should do, full rebuild also. This also allows you to keep a engine block, heads, innards, that you know did run well.
Where to buy, what's the best parts? Again many people = many opinions. Ya want a stock engine, use stock parts. Ya want racing or slightly modified, well that's where each will offer their own opinion and here especially does your "budget" come into play. I myself have done well with stock, and mod's I buy based on reviews and opinions of those deep into cars. NOT the "shade tree people".
I wish you well in your decisions and budget. It is a rewarding experience to say "I did it myself". Good Luck !