Go order a replacement turbo for the skid steer online, you'll pay a little more since you don't have a core return. Next start hacking up the manifold, rerouteing the intake, welding, cussing and with a couple trips to the parts store you'll be in business.
I know somebody has got to ask....what are you doing where the tractor feels so underpowered?I had a L3130 HST that pulled a two bottow plow,pushed a six ft.snow plow ect.Traded for a L4240 mostly for the cab.I do most of my work with the L4240 in medium and toggle between high/low,this plus auto throttle I don't see how you can be underpowered.
There was a person who added a turbo to their Kubota several years ago and posted pictures here some where.
That being said the "newer" 40 series Kubota's are "emissions certified" and I don't believe you can turn the pump up. Which would mean you would have to change the fuel pump. As others have said, will the rest of the tractor take additional power?
It's probably more you are losing power from the HST. I have a L3240 and do regret not trying harder to find a L3540 with the GST. While I have good PTO power, the unit HST isn't as good at putting power to the ground. I have to do everything slower than an equal HP gear shift unit. I have read that you can lose as much as 35% of your power through an HST. So as much as 1/3 of any gain could be lost. I don't know what % the Kubota HST uses.
Mahindra 7520, Mahindra 3215HST, Case 580 extendahoe, Case 310 dozer, Parsons trencher, Cat D6,
Very common for the pistons to be different, the rods, injectors, injector pump and or settings. If you just put the turbo on without changing everything else that is suppose to be changed for that particular engine, you have just taken an engine that has a 100% duty rating and lowered that duty rating. How much depends on the engine itself. Really not a good idea if you work your tractor hard any length of time.
Just saying what you don't want to hear, but it is what it is. Can you do it and everything be good, maybe, but then there is a better than average chance that it pops.