Series Leafers were pretty kuch at the limit of the possible modification when they phased them out and introduced the 90 & 110 in '83 with new suspension, transmission and different engines.
Over the yeras poeple have done loads of stuff to them to make them more useful in modern conditions, and while modern 90's 110's & Defenders were that much more expensive, it made some kind of sense, but these days second hand car market is saturated. Deffy's still fetch a premium, and SIII's are still reletively 'cheap', but the ecconomics of modding them donmt stack up, & impediments of SVA, or is it BIFA or something now, either way, the rebuilt vehicle test to establish registration validity on a rebuilt classic for taxz exemption or safety on a heavily modded custom, really make it a no go before you begin.
and if you DO tackle a series, you start to find that they dont respond well to major or drastic mods, and the bits you THOUGHT you could cheaply and easily source and use from old disco's or rangies dont really, without a lot of drastic tin-bashing and welding....
they respond best to subtle and sympathetic restoration incorporating a few well considered 'minor' upgrades along the way.
For example fitting a 2.5NAD engine from an early 90/110 or sherpa van, or detailing the petrol engine with a high compression ratio 'unleaded' cylinder head, and electronic contactorless distributor, amp and coil from a Montego.
Maybe fitting parabolic leaf spring suspension with gas dampers, and modern tyres, like 235/85Radials possibly on aftermarket, deep dish wheels.
Upgrading brakes to the last of the line TLS Servo assisted drums, from a late 109.
Adding sound-proofing, trim, a cigar lighter socket, and whatever accessories take your fancy.
But MOST of all, the grumbles and niggles most moan about like heavy steering, leaking roofs and windows, sloppy gear boxes etc, can be taken care of through good contientiouse restoration & renovation, basically old fasioned mechanics and attension to detail.
and if you have the luxuary of the time and space to do a full ground up, then so much the better.
and the closer to standard you keep it, especiazlly for a newbie, it should all be, as it wil all look like the pictures in the book.....
which is the 'Green-Bible' AKA the official 'Land-rover Series III Repair & Overhaul Manual....
that should be the first thing you shoulod buy, costing about £20 from all good Landy Emporiums!