Suggested this elsewhere but MkII Polo (82-92 ish) heater is excellent and contained in plastic unit incorporating 3spd fan. Mounting is simple and all that's needed is a little folding (metal) and poss. some heater flexipipe for mating it to Series vents. I haven't fitted one yet but thought it through as my 100" trialler doesn't have a heater. This isn't a problem trialling, but after a heavy shower on the A9 I hit a puddle of standing water (while proceeding northwards at 57 miles per hour,your Honour!)and the cab filled with water vapour (modified tunnel for LT77s(?-4spd on back ofV8) has slight gaps - too small for small children to fall through but I feel an attack of duct-tape coming on!) which all stuck to the screen. I couldn't clear it. The gaps are also handy usually as that's where my heat comes from and temp. control is by opening all the windows.
May not be what you're looking for check it out - they're cheap (from scrapyards) - new matrixes (OE) available for v. little from Eurocarparts or German&Swedish etc.
FWIW, I've run lots of MKII Polos and Golfs for many years, owned (and run(on average)) three or four at a time doing about 75000m p/a (me, she who used to be obeyed, friends and little sis) and I've only had one matrix fail on me - that was in a car that'd stood for 15mths with water (no antifreeze!) in it and a v.small pinhole leak rotted through from inside. Fixed with matrix from another (spares car - 20 mins to swap, 15 mins to bleed - there's even a bleed screw on the side of the unit so 14 mins to heat & open thermostat, 58s to open screw and bleed, and 2s to open a self-congratulatory crate of Grolsch
![Wink ;) ;)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
) about 7 years ago and car (and matrix) still going strong.
I can't fit unit in place of LR matrix as I have a large s/s header-tank there but assuming your machine's standdard(-ish), you could just replace LR unit (higher than both engine & rad so theoretically no airlocks) Unit can even be left unattached for bleeding (bleed screw held at highest point) and then mounted in place afterwards if access/ bleed screw not going to be high-point when in-situ. If you wade you could even mount it inside the cab (cut dash?) to prevent shorts but recirculating air may be a concern (unlikely in standard usually leaky-vented Landrovers!)
HTH