The casting numbers here are for production blocks manufactured from 1986 to the end of GenI/GenII production.
For 350 flat tappet blocks look for casting number 10054727, 14079287, 14088548, and 14101148.
Roller blocks are more complicated because even though the casting number indicates the block is provisioned for a roller cam, it doesn't for sure mean the block has a roller cam. But if so provisioned, a factory roller cam can be installed to one of these even if it currently has a flat tappet cam. For 350 roller tappet blocks look for casting numbers 10243880,14011148, 14088526, and 14093638 these can be a 2 or 4 bolt block. The 880 is the Vortec block it appears in mid 1995 production with swirl port heads and TBI and may have a flat tappet cam but is fully provisioned for a roller in all instances. It appears again in some 1996, 49 state vehicles with Vortec heads and TBI.
A problem you could encounter when hunting the wrecking yards and rebuilders is that there is a flat tappet block and a roller that both end with the numbers 148. 14101148 is a flat tappet truck block, 14011148 is a roller provisioned block.