I have Gibb keys in stock. No, you cannot reach the piston through the injector hole on an indirect injection Lister . Some of the clones are direct injected and can be.
Flywheel in the way? Yes. Is it an issue? No. Use the other one and leave the #1 side off
To find top dead center you first need a pointer and a refferance. Mount the #2 flywheel and lightly secure with a key. Next using a piece of heavy wire, or flat stock make a pointer on one end. You attach it to any handy bolt. Point it at the flywheel rim, the closer without touching the better. Next you need to decompress the #2 cylinder. This can be done by loosening the injector. Next turn the crankshaft so the keyways are at 3 or 9 o'clock makes no differance which way. Now on the number one cylinder you need to block the exhaust valve open as shown in the attached picture, not just a little bit open but as far as you can. Use a vise grip on the rocker to pull it open. Next carefully turn the engine until the piston hits the exhaust valve. Put a mark on the flywheel at the pointer. Next turn the engine the other way until it hits again. Place a mark under the pointer. Care fully measure between the two marks. Divide measurement by 2. and place a mark exactly halfway between. Cylider 1 is TDC when at the pointer is at your TDC mark. Remove the block holding the valve open. Rotate the engine to your TDC mark.