low compresion on back 2

hi every one

i have just bought a 3.9 V8 discovery 1 Auto 1995 LPG converted. have been told it has a missfire and a compression test was done and back 2 were low on compresion. to me it runs fine and it does not back fire, or give any signs of there being a problem, but does seem rather slow for a 3.9 and very thursty. does not run hot and starts every time.
i am going to replace plugs, leads and dizzy. fuel pump and filter to c if that helps, my mate says its prob worn cam or valves. has anyone had a similer problem any info would be a great help as if it is cam thats a magor expense i cant afford right now as been quoted over £400 as its a big job

if it runs ok leave it alone and drive it, they are not super quick as they are a 2 ton brick.

if swapping ignition parts make sure you use only gen lr in gen lr boxes or magnecore

ok thank u

Let's start at the top
LPG kit mono or multi point injection?
How many miles?
Genuine dealer ingnition parts are now total gash but am sourcing please be patient!

Ok issues if it has been run predominantly on gas it could have the beginning or piston ring stickage to the pistons causing a poor to low compression when you did the test did you drop some oil down the bores did it improve or get worse?

i did not do the test a friend did so not sure how or what they did. all they said was its low on compresion on the back 2 cylinders. it seems to run fine and does not over heat. but i am no machanic but dont want to continue running it like this if its going to cause damage over time after all i have only had it a month so dont want to break it just yet lol. i have been running it on gas as much as possible, but there r days when its on run on petrol ie when gas runs out lol. it runs fine on both, i did say it was slow but now i am used to it it picks up fine. my friend to try towing with it to c what it does, ie if temp rises or it struggles to pull. i may just have to book it in at duglas motors for a proper test that way i will know whats what and if its worth keeping as if it is worn cam or valves its not gonna be cheap to fix just my luck find a disco i Really like and it has problems, if it was a rust bucket it would run forever llol i know its hard to give advise without knowing or driving the car. but any usefull info would be great
dont know if its mono or multi point :/ could take a picture of engine if that will help
its done 157k

just had a quote from Douglas motors to do a diognostics on both petrol and LPG system £100 so think i will do that and will hopfully get an answer as to whats going on, as its also using petrol when switched over to LPG.

at 157K and no history then first stop is cam and followers.
if it has done majority of its life on gas suspect rings sticking to pistons causing low compression too