"Is it acceptable to pay the tax on the conversion from withholdings from a monthly pension spread over the entire year rather than doing estimated quarterly payments?"
Yes. By default, both income and withholding are treated as having been received and paid evenly throughout the year. The source of the tax withholding is irrelevant.
"If done by quarterly estimated payments, can the tax bill be spread over all quarters from the conversion or must the entire tax bill be paid in the quarter of the conversion."
Because income, by default, is treated as received evenly throughout the year, estimated taxes can be split into equal payments for each of the tax quarters.
Withholding, by default is treated as paid evenly throughout the year no matter when it is actually paid while estimated tax payments are treated as paid when actually paid.
