V6 Cylinder head removal

[zimb1]

Hi everyone Just bought my V6 Bongo this year and despite a lot of minor repairs and servicing to get it to good condition I had an overheating problem and broke down on the M4. After we got to a service station the RAC man did a block test on the cooling system which indicated exhaust gases in the system meaning a leaking head gasket or cracked head or block. When I got the vehicle home to be sure I did the test again with a test kit I found online as it can still run and the leak is not bad. Their diagnosis was confirmed so have no option but to remove the head(s) which brings me to my questions.
1. Is there a way to determine which head is leaking or is it necessary/advisable to remove both heads?
2. Can the heads be removed with the engine in situ?
3. Has anyone done this job or know anyone who has and can give me any advice on the procedure.
I am a qualified mechanic although haven't practiced for a few years and have the workshop manual so intend to do it myself but any help would be appreciated