1 - Re the "cheap crank" - I run a Cast Eagle in my 12 sec 390 - So far no issues but I had to index it plenty and the casting was pretty average. I'd use a forged MP or SCAT crank next time.

2 - Re the "merit" of building a 390 - they make way more ftlbs than an = 360, so for an E Body they make sense.

Be prepared to sink some $$ into the heads however....they really need to flow 250 @.550 minimum.

3 - Re - the comparison with a BB - the SB strokers buzz up so fast - they're making max torque way quicker than a std stroke 440 with the same cam - thats the beauty of them.