Title pretty much says it all:

Looking to build a healthy street/strip small block to power an E-body, backed up with a 4 or 5 speed manual trans.

Clearly, the budget will require some swap-meet/Craigslist shopping, but I'm not in a rush.

Aside from a 340/360 base for the cubes - what would you suggest? (assume that the core motor has already been purchased)

Start with a 360 that runs well. Upgrade (performance valve job) the heads, replace cam, intake, carb, and headers.

assuming the core motor has not been bought, I'd pick up a magnum 360 and start there.

assuming it has, I'd go 360, reuse the stock crank, redo the stock rods with ARP bolts, use some KB167's,

for heads, I'd probably go with the RHS/indy magnum heads that hughes sells for ~ $900 assembled. I'd go magnum because you can find nice rockers cheaper (use SBC style rockers). rockers, I'd probably use scorpions, 1.6 ratio

intake, I'd use an eddie RPM air gap.

cam, if you want a hydraulic, I'd go something like a comp XE275HL if you're stuck with a flat tappet. if you start with a magnum, you could use a roller cam reusing the stock magnum roller lifters, and I'd use the comp XR274HR.

carb,intake,cam,headers,4.10+gears, & 150 shot of NOS. done.