First of all, there's nothing wrong with your 2 bolt block just because its a 2 bolt main. 4 bolts are nice but its well documented that a 2 bolt with main studs will handle 500 HP no sweat. Now lifters in the oil pan . . . there's a problem
Personally I would look into both building a stroker bottom end AND getting some new aftermarket heads. 400+ HP is easy with aftermarket heads in a 383 and still very driveable.
The things I would skip are: extra cash for a 4 bolt block, forged bottom end parts, fancy chrome or aluminum stuff.
The things I would invest in are: aftermarket heads (ProTopline iron with 200c runner 72cc chambers), good machine work, and a balanced reciprocating assembly.
Here's a low buck combo suggestion for you ---
redo your 2 bolt 350 block, just have it checked for cracks, bore it .030, new freeze plugs, cam bearings, and hot tank it. (skip align hone, and decking if you don't absolutely need it) $300-400
Eagle 383 rotating assembly with KB flat top pistons, 5.7" SIR rods, cast crank, flexplate, harmonic balancer, rings, bearings. $1100 (balanced)
ProTopline 72cc iron heads with 200cc runners. Use the new Felpro .018" thick rubberized steel shim head gasket. $850
Comp 280H cam and lifters. Comp 1.5 roller tip rockers. 1 piece moly pushrods. $160 cam kit, $100 rockers, $75 pushrods
Performer RPM intake and Holley 750 list O-3310 carb. $120 intake, $230 carb
1-3/4" Hedman headers and 2-1/2" exhaust. $300
. . . and allow a few extra $s for gaskets, oil, and other parts I didn't mention. This combo should beat the 400 HP pretty easily and still be mild enough for commuting. 10.0:1 compression ratio so it will work with pump premium.
Just my opinion