I haven't dealt directly with BBM, but my observations are that they probably deal with the same foundry delays and cash flow issues as anybody else in the FE business. Speaking from personal experience with my intake adapter castings, sometimes the foundry will promise delivery in 6-8 weeks and take much longer; this delayed my initial batch of intake adapters by a total of nine months a couple of years ago.
One observations specific to BBM is that when they first got going on the block and head project, on the FE Forum Doug criticized many other FE manufacturers (like Blue Thunder, for instance) for not having the parts available for purchase. He claimed the FE world "deserved" to have the parts available all the time, and BBM was going to be sure that happened. Yet they have consistently run out of blocks and heads, leaving people waiting for months at a time. I'm sure the realities of short-run manufacturing and cash flow management have hurt them, but to make a promise like that and then leave people waiting is hypocritical and not good business, in my opinion.
By most accounts the products are high quality, so if you need them, as Howie says, get in the queue and hope for a near term delivery...