Hi AJ453:
The conversion of you oven is simple just the changing of an orifice and a spring any service co. should be able to do that .
As to How much propane you will use. Depends on how much product you put through it,
Your oven running flat out for an hour would burn 135,000 BTU There is prox. 91,500 BTU per gal. of propane. Take a WAG and estimate you will average 85% of capacity per hour you will burn 11,4750 per hour
that’s 1.5 gal of propane.
George G Mills