Hey Jim,
I did not intentionally knock your engine setup, if i did i appolagise. What i was trying to say was that thru the yrs. of experience is that i prefer to run the smaller main bearing. I have run stock 400 blks for yrs. and still do have a 377" stock blk. I have since the 1980's ran bearing spacers with the 400 blks.with success and the engine above (Dart Lil"M") is my first adventure into a true race block, but i bought it with 350 mains. I will say that with the gearing in my car if i can get it to perform the way it should, it will be turning, close to 8,000 RPM's, but only 5.50 sec. 1/8mi.@3250lbs, if it don't i'll be the laugh of the day. Only time will tell.
Zip.