FJ60

There is not much you can do to make these go faster.They are based on a 1953 chev truck motor so they are close to their limit.They dont like going over 3000 rpm so adding extractors,aftermarket air filter,which only start to work at higher revs, is a little pointless. A 3 in body lift and 35in tyres is heading into competition territory. The body lift would require the steering , brakes and drivetrain to be modified.You are right the tryes would change your effective gear ratios.You would have to change diff ratios or transfer box to be able to use them.
My tip is to do a 2inch suspension lift with 33 inch tyres which should cost around $3000 .It will look good,perform well and leave some money for maintenance.
If that hasnt put you off,a small block chev,350 or 383 ci conversion would be best if you want to go ahead with the body lift and 35s.
Outer limits 4x4 landcruiser forum is the best place to ask advice on these mods.

yeah 3 inch body lift.......nah.....to hard too much bucks.......go the 2 inch suspension lift and 33 inches as suggested.......you can do a 1/2 inch body lift by just putting in spacers cut from steel plate without changing steering brakes etc etc
thats what im running and it was cheap and works pretty good the 31s you have are a smaller than the stock tyre so the 33s will bring it back closer to what was original......my 75 with a 3F and 33s does 110km/h at 2300 rpms......comfortable for old petrol tojos.......and forget the all terrian tyres go the muddies makes a big difference if your gonna play in the bush as you say......hope you like noise and petrol stations get used to em both ...all petrol tojos chew the juice but the advantage in power over old diesels tojos eg. the 2H diesel offered in mine at about 70kw versus the 3f petrol at 110kw is big and the old diesels dont like turbos much so i couldnt see why i would pay more for and old diesel snail...110kw is still more than the modern 1hz diesel no turbo..offered to date at about 94 kw as long as you dont mind the fuel costs and dont plan to swim the truck say deeper than 1metre or so it should be a good toy.........mind you if i was setting up a long distance tourer...and not a weekend bush toy the 78 series td rv would be my chioce for power, fuel economy and reliability..... anyone want to lend me 65 grand????? or if there,s a nice tojo dealer out there who wants to donate one
give me a call......ps i will take any colour

yeah mate the mtr,s are a mud terrain....i was just saying dont bother with all terrians
yeah ive heard of topdog.......and the stock rubber that the sixty came out with is equivalent to about 32 and 1/2 inches

I have an FJ60 Pretty similar minus the immaculate ie OME shocks and springs
on 10.5 by 31's with a 2f , 5 speed and 4.1 diffs. It has a set of genie extractors
on and comes onto the pipe without flutter (read no dead spot) at about 2000 rpm and pulls strongly all the way to 4000. Don't think it helps the MPG though as I get 24 - 27 L to the hundred witha lead right foot in town

Am going through the process of sorting tyres out for the truck
Originally wanted 33 by 10.5in (supposedly good combination) and could keep the 7in wheels but everyone says go to 12.5's on 8's

My logic says that a 35in wheel has a 2in bigger radius so therefore if a 31in fits stock then you only need a 2in lift to get the height clearance under the guard
Turning clearance might still be an issue though

I have made 35mm lift blocks in al. will be throwing them in this weekend 16/17 Nov Everyone says its easy but fiddley.

Figure to try 35in tyres see if they fit with Ome lifted spings and 35mm body lift
will let you know