The pleasures of a hand-built car!
The oil pan is quite strong and will easily support the engine when it's on the ground.
First, try raising the drivers side (left side) of the car using the jack placed on the left of the oil pan. If you're concerned about damaging the oil pan, just go easy and watch the pan from underneath. Use a block of wood to cushion. You should not need to raise it by much and the engine should rotate a little and should give you enough room to wriggle the bolt out.
There's a bit of 'flex' to the engine mounts and in truth, it's the weight of the engine that keeps everything in place. Whilst you're 'playing', inspect the mountings for signs of perishing as, after 44 years, they might be starting to degrade.
Last edited by Cheshire_David; 17/02/15 02:28 PM.