The engine needs to be rotated almost one complete revolution to remove the bolts, one at a time, from the flex plate to the torque converter. Only one or two of them can be accessed at a time through the inspection cover at the bottom/front of the transmission.
Something sounds not quite right here. There is an easy work-around in which the torque converter gets pulled off the transmission and stays with the engine as the engine is removed, then the bolts can be accessed later to remove them.
It is not customary to buy your own parts and ask to have them installed. That's like bringing your own food to a restaurant and asking them to cook it for you. In this case, I find it very hard to believe the person you talked with at the shop didn't ask you right away why you wanted the engine replaced. You wouldn't walk into a hospital and expect to be treated without them asking you for what. When I spoke with a customer who wanted his car aligned, I always asked him why, so I knew if it was just a maintenance thing or if there was some problem I needed to look for. Very often people think a transmission or an engine has to be replaced when no professional actually diagnosed it as such. Any reputable mechanic will check it first to see if that major repair is really needed, and gladly tell you the problem is much less-expensive to solve. I can't imagine someone not asking why you wanted to have the engine replaced.
Given the age and mileage, as long as this work is being done, consider having the transmission's from pump seal replaced right away. They become hardened from engine heat over time, and regardless whether the torque converter comes out with the engine or it stays on the transmission, that seal is going to have unusual pressure placed on it that will deform it. If it is still pliable, it will just go back to its proper shape when everything is reassembled. If it has become hardened, it is likely to crack. That will result in leaking transmission fluid and the need to remove either the engine or the transmission to get to that seal, when that could have been avoided by just replacing it as long as they were right there. That is a round metal ring with a rubber lip seal that rides on the hub of the torque converter. This extra service should take about 15 to 20 minutes when everything is already disassembled.
Tuesday, February 9th, 2021 AT 2:25 PM