lifter clatter on startup

hello, I built a new 383 from my old tried and true 350. It was a perfectly running engine , just wanted more power. The new engine is all I had hoped for except I get lifter clatter on starting. But only if it sits for more than 8 hours. also low oil press for up to 2 seconds, after sitting. once started oil press cold is 60 psi, at 750 idle and 200 oil temp press is 25. at same temp at 1000 rpm, press is 40. I have replaced the hyd roller lifters, I had reused my originals, wasn't having a problem with them before. checked for too stiff valve springs, they have 100 lbs seat pressure, didnt check compressed press, they are not hi rpm springs. Put in screw in plugs on the ends of the block and no I didn,t restrict any of the intersecting oil galleries. Tried an oil filter with an anti drain back valve in it. tried diferent weight oils. Like i said i only have this problem after the engine sits overnight. Had the block machined by speedomotive and noticed some one took a hone to the lifter bores. The engine only had 75k miles and was a hyd roller lifter low rpm tpi L98. i wondering if the bores are too big. Noticed some play in the lifter to bore interface when i assembled engine. But I think they are plenty of engines like this around without my problem. some with any ideas?

Hello, thanks for the reply. I had reused my stock gm roller lifters in the new engine. I never had a problem with them in the old engine. same block. I did take them apart and cleaned them . all parts went back in where they came from. already replaced them with sftermarket lifters.