As already stated, BP springs & shocks are good quality and you can fit them with no qualms whatsoever. If you are unsure what you might want long term then just go for the OE spec springs & oil-filled shocks, they are a very reasonable price and put the vehicle back to standard and from there you decide if you ultimately want to upgrade to gas shocks, std height HD springs etc.
Before you start you do need to discover if castor correction radius arms of non-standard turrets have been fitted but a visual check should confirm that.
With regards to replacing springs & shocks I have never found it the slightest problem, regardless of what springs have been fitted (even +2inch) and have certainly never required the use of a lift or spring compressors. ***
It goes without saying that when lifting a vehicle on a jack, make sure it is chocked & stable and always use proper axle stands, not piles of bricks! *** Do one station at a time, not axle pairs.
Rear. Jack up vehicle and support under chassis. Remove wheels and lower & support axle using jack (watch that brake-line!), remove shock, lower axle again (keeping an eye on that brake-line), remove spring, fit new spring & shock, lift axle, fit wheel, raise chassis and remove axle stands.
Front. Remove plastic access panel from inner wing (and whatever may be positioned above it). Jack up vehicle and support under chassis. Remove wheels and lower & support axle using jack (watch those brake-lines!), unbolt shock, remove turret, remove shock, lower axle again (keeping an eye on those brake-lines), remove spring, fit new spring, shock & turret, lift axle, fit wheel, raise chassis and remove axle stands.
Very brief but I think they are the steps I always use.
Goes without saying that some fixings may be corroded (thinking shock & turret mounts here) so some prelim work with penetrating oil will be in order plus always grease on reassembly.
The photos below are about 18-years old and show when I fitted Scorpion Std height HD springs & DeCarbon gas shocks to my 90.
I had spent a long time researching what I wanted (it was an ex-MOD FFR and the original springs were almost rigid on my lightly loaded vehicle) and I have to say that the set-up I chose was as close to perfect as I could get. It served me for many years until eventually one of the rear springs snapped so I had to quickly obtain replacements and that is where the problems started as Scorpion were no-longer trading so I was trying to find equivalent springs from elsewhere. What didn't help was that by then the layout of the vehicle had also changed and the weight wasn't the same so what suited years before did not suit now. After experimenting with several set-ups I eventually settled on BP OE springs at the front, Bearmach Std height HD rears and Koni Heavy Track gas-shocks, this set-up has now been on for about 5-years and is doing everything I could ask of it.