Well I am building an engine for my 69 K5. I have to decide whether to build the 355 block I have now into a 383 or build the 400 I have here. I am basically looking for any opinions on the 400 that anybody has as far as reliability with the siamesed bores etc. I know you have to drill steam holes in the heads for the 400 but I figure you have to clearence the 350 for the crank anyway so there is machining involved in both. Anything else I am missing.