Heads are where the power is at. Not sure of your budget or how far you want to go on it but I would do a full rebuild.
Bore, hone, hot tank..
Buy this rebuild kit
And upgrade the kit to these parts for these extra charges
Frost Plugs: Brass $8.37
Cloyes Timing: Cloyes Double Roller 3 Key-way C3023XSP $11.37
High Volume: Oil pump (must use oil pump shaft with steel pin sleeve) $10.25
Crane Powermax Cam & Lifters 2000-5000 RPM #113942 272/284 adv duration .454/.484 lift Valve Springs must be changed, Not Computer Compatible $110.99
Performance Piston Upgrades:
Sealed Power/Federal-Mogul Hypereutectic Pistons (flattop) # H345NP $18.28
Sealed Power/Federal-Mogul Moly Coated Rings $19.01
Oil Pump Shaft: High Volume Oil pump shaft (must be used with high volume pump) $6.99
Set of 8 Connecting Rods with ARP Bolts Scat Forged I beam 35700P $159.99
Scat New Crankshaft Cast/Steel #910442 2 Piece rear main $169.99
That scat 9000 cast crank is stronger than GM forged and weighs 5 lbs less than GM cast.
Rod bolts are the most stressed part in the whole engine, need ARP bolts for sure. It's just as cheap to buy the above rods with bolts installed as it is to buy bolts and have them install. When you change rod bolts you must have rod big ends resized and thats a $60-75 job plus the $40 rod bolts
Along with that kit add a set of fel pro 1094 head gaskets (4.100" x .015") and that will get your quench height to target .040" and help compression.
Those pistons and head gaskets will give you 9.98:1 with 64cc heads and 10.18:1 with 62cc heads
For heads I would do one of the two.
GM 1996-02 vortec 350 heads reworked
Or Brodix IK 200cc heads
The vortecs will run you about $500, the Brodix will be double that, but will gain you about 20 HP over the vortecs and weighs 40 lbs less
Top that off with an edelbrock performer RPM intake, 750 cfm carb
Headers, dual 2.5" pipes
HEI dizzy, set timing to 12* at idle, 32* total at 3,000 rpm
add a K&N air filter
and you will have you one nice engine thats pushing past the 400 HP mark and truth be told closer to 450 HP