To start a stock 390 block was rated at 375 hp with 6090-h heads mostly unless you had a gt 390 with gt heads I think was 6090-R .

You could add 6090-N heads which were 428 cj heads and a cj aluim intake with headers to boost a 390 pretty well . A stock 390 say 4 speed the tranny will not shift over 5000 for the clutch spring will not disengage to handle the rpms .

To get higher hp why would anyone goto trouble to build a motor stock with intentions of the motor having high hp without a strong bottom end ? All that is no good unless you use a good set of rods , say aries pistons and a stroker crank of choice .

If you going to the trouble to build a fe find a webbed 390 block or a 428 block . Those will hold up better and use a scat crank which is a cheaper stroker crank . Stroking a motor is a great way to get higher horse power for the money .

If going with a automatic you will need a stall converter , size depends on how strong your motor is going to be . You can get by with a 2800 stall pretty cheap .

Spped sho is building a motor for me to go into a 66 fairlane , 4 speed car . Never run a strong motor without useing a good scatter shield bellhousing as such lakewood . If the motor would exsplode that will keep your legs if it blew back into the car , I've seen a man loose his legs when motor blew .

My block is a 428 and still we x-rayed the weak side of block to sleave it to the weak side then line bored it . A good stroker crank , lamons rods , aries pistons ,apr bolts ,pinned bearings , better oiling cross drilled . Heads are by dove aluim but a good flowing cj head would do well . I use a tunnelwedge intake , hooker headers .

Depends on how much money you wish to spend , if limited buy parts and save them . When you get all good parts then have it put together . As for your question of an answer , around 375 to 400 is what you will get out of a stock 390 . Start additives on top the stock block willnot handle the increase hp without a good bottom end . All is about how much money you can spend but mostly finding great deals on parts , they are out there .