That F350 is an 82-85.5, It has the Ford script grille, with the indepent front suspension, 80-81 have ford in letters on the hood, with an eggcrate grille, and, the 85.5 up F350 4x4's have a solid front axle...
For 80-86, you're looking at a 300, 302W, 351W(post 1982), 351M in through 82(can be found through 84 though), and 460(7.5L, not 7.3) the 6.9 Diesel was introduced in 1983. I'm not sure what Aussie engines were offered, but, I have seen 80-86 Aussie trucks with X-flows.
For the older trucks, you will find just about anything Ford built, depending on what year it was... Clevo isn't quite clear in his explination, of what engines were avalable when...
The 302W became avalable in 69½(went EFI in 1985) and was in ford trucks without skipping a beat until 96, when they switched to the mod motors.
The 360 and 390 FE big blocks(same block) came online around 67 or so, with the 360 replacing it's 352 CI predecessor(also FE series.) They were offered through 76, With the 400 coming online in 76, followed shortly by it's little brother the 351M. The 400 was offered until 1981 or so. The 351W 2bbl came out in 82, and, the 351HO 4bbl came out in 84, and replaced the 2bbl 35W by 85½(went EFI in 87). The 460(EFI in 87.5) was first offered in trucks in 1973, and was in production through 79, but, only avalable in 2wd trucks, it was out of production in light trucks until 1983, when it was re-introduced alongside the "new" 6.9L Navistar diesel, and, was offered in a 4x4 from the factory for the first time.
The base engine through all this was the BB6, the 240 from 65-73, with the 300 optional, and, the 300 became base from 73 on, as the 240 was dropped from production.
For transmissions, the Ford C4 and C6 automatics backed most, if not all of these engines, with the AOD becoming avalable in 80 behind certian 302W equipped trucks.
For manual transmissions, until the 80's, you will find either a 3.03 3 speed manual with a column shift, or a 4 speed with a non syncronised compound low(B-W T-18/98 or NP 435.) From 80 Up, you will find those three, with assorted 3 speed/od boxes and the T19 4 speed(syncronised compound low) thrown in the mix. The F-Series did not gain a 5 speed until 1987 in the F150/F250 LD, and, 87.5 on the F250HD and up.
A Short Box Flareside 80-86 F100/150(100 was dropped in 84, with the light GVWR trucks just becoming F150's) 2wd weighs in at 1600KG or more, and, that's about as light as you're gonna get.
Sure, you can build a decent performer out of one, but, keep in mind, it is a truck, it's heavy as old hell, and as aerodynamic as a brick.
My F250 probably weighs in excess of 2500 KG empty... But, it is a 4x4 with a 460(335KG or so dry), a cast iron 4 speed(good 80 KG), and a full floating rear axle that weighs a good 275 KG on it's own, not to mention the 4x4 related bits. I know for a fact that the framerails in it are a good 6.5mm thick(this is why:
http://www.bigblocksix.com/f100swb/f250/IMG_0019.jpg Kinda shortened my chassis) It's far from something you'd build a go-fast machine out of, but, if you want to tow your house through a bog, it's up for it. For my engine/transmission/axle combination, max GVWR(truck and load combined) is 4000KG, the max GCWR(gross combined weight rating, truck and trailer) is 5216KG, if I had a slushbox, it'd be 5443, with 4.10 gears and a slushbox, it'd be 8391 kg. It's also built to stop it... The brakes on the front have 12" discs and dual piston calipers, rears are 13x3" drums.
My F100 OTOH, only had a 2150 KG GVWR, and, a 3000 KG GCWR because it was equipped much lighter and had much smaller brakes, and a less powerfull engine(a 'Canadian' 300.) I don't know why the 300 got the Canadian name slapped on it... I have seen many Cleveland OH built 300's in Canada, and have only run across 2 Windsor bult ones. The 300 was produced pretty much the same from 65 up until 1987, when it received MPFI, and, it was in production as a truck engine from 1965 through to 1997. It was built as an industrial engine(still carburated) until 2000.
As for room under the bonnet, well, even with the 460 with all the a/c junk, there's room:
and, with a 300, it's bloody spacious:
Mind you, those are both 80-86 trucks, which are less roomy than their predecessors.
For comparison, this is my 78 with a 351M(I think you guys were lucky enough not to get that engine...)
You should see what a 302W looks like in there...
Hows that for a pile of semi-organised, semi-usefull info typed by a silly Canadian at near 2:00 in the morning?
Evan
and oh yeh y r they still so dam expensive for an old car???
If you don't mind a custom inferior, buy one that's a bit rough inside, and play around some. 
CHEERS