Here is some information kindly contributed by Colin Jenkinson of Australia:

Just a note of caution on the V6 3.4 Litre engines I have seen offered on your site.

I have just finished fitting one of these to my Taimar here in Australia, here is what I found with the crate engine supplied to me.

The engine was not new but remanufactured with 60 thou pistons

I had the engine balanced to match the old flywheel and pulley.

The engine had been hot tested (started and run) unfortunately they did not pre lube it correctly and scored the rockers and shafts.
Rockers are available from South Africa, Rocker shafts appear to no longer be available.
The engine builder who balanced the engine said the rocker tips look as though they had done 100 thousand kilometres and not been refaced.

The oil pump had imperial bolts screwed into metric treads for the oil pickup, I ended up installing a new oil pump to repair the damage.

The exhaust port bolt holes are spaced further apart than the essex engine a new header plate is needed or new exhaust is required.

I modified a new JP exhaust system to fit, nicely ceramic coated as well.

I have a digital file for a laser cutting machine to cut new plates if anyone needs it.

The front pulley retaining bolt is metric not imperial as in the Essex engine.

Otherwise it will bolt straight in!

My understanding it has a stroked crank as standard but I did not check the stroke on my engine.

3.4 litre was cast into the original rocker cover so I have no reason to doubt it.

I also understand a 3.0 litre version was made so I guess it is possible they swapped cranks shafts around.

I understand Burtons and others were selling the cranks from South Africa then modifying Essex motors but I believe supply has dried up.

Regards
Colin Jenkinson