I recently came across a virgin 400 block and am kind of erie about using it for my next build up considering the cooling problems I've heard about do to the siemese cylinders. I know I can drill steam holes in my heads but what other tricks are their. Has anyone had good luck with cooling these blocks?

I'm planning on about 10:1 compression and iron heads.

I currently have a brass/copper 4 row radiator, flex fan, shroud, and a flow cooler water pump.

Will this be alright in traffic on a hot day?
How bad are the cooling problems?

nope, sorry, those blocks are junk. i urge you to send it to me, so i can make sure it never sees the streets again. i'll take care of the postage even. ;)
j/k, those cooling problems are old wives tales, as far as i'm concerned. several of my buddies and i run them (hard) with no problem whatsoever, without the steam holes even. the only reason i would even drill the steam holes is if it's going to spend the better part of its life idling around. grab that block and build it like any other smallblock, and enjoy the bigblock torque it gives you in return.
that is is you don't want to take me up on my previous offer :D

Had problem with the 21" 2 core... went with w 21"3 core, new fan and shroud... problems gone. I think the 2 core was old and clogged,the shroud was cut some when I bought the car and halves cable tie together. Had to go.

Hmmm... I collect that kind of junk, too!!!! Many years ago, I put a 400 in a '67 ragtop, used a new stock 2 row radiator 160 thermostat, and 12" electric fan. Would heat up some (210-220) sitting at red lights, otherwise ok. You won't have a problem. Da beast ran 13.2 @ 104, open 3.73 rear, streat tires and mufflers, had a torque curve like Montana... Would love to find one for my '68...

Thanks for all the help everybody, but I think I'll hold on to this one. I figured those heating problems were a bit exagerated.