I used to build engines to pay for my racing addiction. One of the reasons I gave that line of work up was the fact that GMPP (General Motors Performance Parts division) was eating my shorts on builds. Chevy could sell you a factory warranted engine for less than I could buy the parts at wholesale and then have machine work done to used parts. Chevy could grant a factory warranty because it was a brand new engine built with new parts on an engine stand the same way I did it (only "Hecho en Mexico" to save on labor).
Let me elaborate on the difference between a factory warranty and an insurance policy as offered by some reputable engine builders. A factory warranty means if it breaks in the first year you tow it to any GM dealership and they will install you a brand new engine in your car, within hours or at most a day or two of dropping the vehicle off. It doesn't cost you a dime other than for the wrecker. With the insurance policy you pay up front for the repair of your motor with the cost to you dependent upon where you have the work done. You then file a claim against the policy with the insurance company and hope that they will pay most of it. Being as how insurance companies hate to pay out they will look for ways to weasel out of the claim or offer you a reduced payment in the hopes that you will settle.
Just because I said that a GMPP motor was built cheaper than I can build one and turn a profit doesn't mean that they are cheap. A 383 short block will run you $3,500 for a forged crank with four bolt mains in the bottom end. This allows you to keep your old heads and intake to retain the appearance of your original engine.
Chevrolet Performance 19332527: 383 Short Block Assembly Cast Iron Block | JEGS
Or you can buy a ZZ5 350 short block for $2,500:
If you do not mind center bolt valve covers, a brand new complete 350 cranking out 400 horsepower in a ZZ5 Fast Burn aluminum headed Vortec engine runs you $6,500.
Chevrolet Performance 19301294 ZZ5 Turn-Key Crate Engine
Cast iron heads drops the price and Chevy makes four different versions of the 350 differing in the parts they are screwed together with.
If you want a tamer 350 you can buy a stone stock brand new warranted GMPP engine as found in pick-ups and full size cars for $1,550 that will still make more torque (304 ft/lbs.) and horsepower (250 horse) than your base 327 engine that you can keep to sell with the car in the future. The all new engine is designed to run on pump gas regular which your current 327 isn't (even if it was the base 250 horse it requires regular leaded gas that had an octane rating of 96).
These new engines also don't leak oil the way the old ones did which is why they have the center bolt valve covers, instead of perimeter bolts that are usually over tightened bending the tin which causes the leaking.