Advise on many bits of a 1971 2a 109 2.6

Hi all.. im new to this forum and am about to post a hello in the intro bit but anyway imprtant bits first..
Ive just come into ownership of my first landy.. a 01/01/1971 Series2a 109 2.6 six cylinder beast... alright i know the engine isnt te pick of the bunch etc but it was free so im not gonna moan plus it goes stops and leaks like a landy should! Anyway back to my questions... be warned could be a few!
First off is there anywhere that sells lead free cylinder heads for this engine?! only place on the web ive found that even stocks parts is john craddocks. Is it gonna destroy the old girl using unleaded and an additive? although with john craddocks only asking £83 for a cylinder head im tempted! ideally i'd like to up the performance a little so any one know anyone who stocks performance parts for them? Also my gear box although working isnt going to last for ever.. i think im right in saying its the same as the other series ones but bell housing is different.. if im wrong please tell me! When it comes time to replace it should i consider one with say +32% high range gears for better manners on longer trips or would this be too much for such a big vehicle any opinions welcomed... also where can i get one! everyone has a million and one options for the 2.25 but 2.6 is sadly missing out! Basically im after any options for improving its on and off road ability. Oh and any tried and tested weather leak solutions! well its a land rover so reductions! Oh final one is does anyone sell a lock and ignition set that can all be used off the one key.. all my locks are broken and the ignition is loose. Cheers and heres to many answers and probally a million more questions.
Joe

Hi i have also just joined and have been serching for any 2.6 6cylinder related stuff! So a bit late in replying to you but Im running a 6cyl beast and was told from a rover p4 car specalist that the cylinder head being ali allready has hardened valve seats in and is fine on unleaded!

i've only ever driven one 2.6 and about 3million 2.25's the 2.6 i drove was a gutless piece of ship. i have no idea if they are all as bad as one i drove but if they are i'd say changing engines even to the 2.25 would be an improvment.
as i said i've only the one for comparison.
you can pick 2.25's for pennies on e bay and parts are easy to get and fairly cheap. of course you could always bung a v-8 in but thats more work!