I noticed the crankshaft flange has a SS sleeve on it, thats why the rear seal housing can not pass through.
The long blocked was manufactured from Mabbco, is that sleeve a normal thing?
I just purchased a GM 14099090M long block to replace my 14099090, the rear main seal housing 12555768 pulled from 14099090 is too small and can't fit in. I am have difficulty to find the correct part # for 14099090M, most listing just post model of vehicle and can't confirm the block number...