If you are building the engine yourself?
Find a good machine shop,buy a journal.
If you have the time to hand fit each part(basic blue printing) You will have a very good reliable engine when finished. Find the heads you want to use,doesnt matter as long as the castings are good quality.If you decide to use a stock cast iron head,find a set that will yield no more than 9.2:1 CR.Before you purchase or machine the heads,match the pistons from a catalogue of your choice.Post part numbers and have the math guys help with exact fitting.
This means you need to plan the boring and decking of the block to extract the most power and fuel efficiency as possible.The cam specs will be factored in at that time.
The money you spend will be mostly on block and heads,premium machine work,balance the engine.
easy part now is deciding on the bolt ons you like. carb/manifold/exhaust
If you take the time and set your goals reasonable for power,,,? you can use cast or hyper pistons, a flat tappet hydraulic cam and still get an honest 350 HP