How many fuel pumps?

I've just bought my first Land Rover, a 90 of 1986 vintage and look forward to tidying it up and put it to work.
It has a fuel supply issue in so much as it will idle all day long but will stop in its tracks if you drive any distance only restarting after much cranking and bleeding air out of the system. The last owner fitted a new lift pump in the hope that this was the problem but with no success.
I am in the process of working through the supply from the tank and have stripped out both the supply and return fuel pipes which were horribly corroded and patched in various places with rubber hose, I've also removed the sediment bowl as it was corroded and porous but I was surprised to find that there is an 'in tank' fuel pump (with a really cruddy filter gauze) as well as a lift pump on the engine.
My question is (at last!) is this normal to have two pumps as I've never seen this arrangement on any vehicle that's been in my care before.
Once the running side has been sorted I can then get on with that rusty bulkhead!

Have you...before doing all this fine work...changed the fuel filter?

I had similar problem with mine when I got it.
I replaced all lines, cleaned tank, replaced the filter this solved it for a week then it died
replaced lift pump and off we went again
and to this day*touch wood* its still going strong
I didn't have a tank pump, mine is a 87 lr 90 2.5TD.

Oh btw to mke bleeding easier, add a fuel bulb priming pump, before the filter.
I gaurentee this will make you life easier

New filter along with new lift pump by last owner, the fuel pipes definitely need changed and will be after a new sediment bowl arrives. Just wondered why two pumps.