Yeah, not too sure about the motors from the company on that link. I don't know them nor have I had any experience with them but as Tony said, spares are extremely difficult to get, even from the USA. Here in SA it's only used spares available besides things like after market bearings pistons, rings and gasket sets etc. You cannot get new cranks, cams, cam followers, rockers, heads, water pump, oil pump and (i think) valves.
So where are they getting the spares to re-con the motors? At those prices I very much doubt that there are any spares coming from the USA and that the motors are not properly re-built. I suspect that they are given a lick and promise with reground parts only "where necessary" to use his own words.
I am in a position where I have an SFA with one of those motors that is lacking power with a very noisy valve train. We've tried setting the tappets, but it hasn't helped.It's been that way since I bought the vehicle and I was thinking that if the motor gave in I wouldn't bother with it, but replace it with something else like the 5VZ Toyota 3.4lit V6 (Prado motor).
Now here's where I got into a battle of reason ..... the original motor conversion was done by JT Conversions and the job was done properly without any issues that often arise with such endeavours. The motor had been stripped and 'rebuilt' by the previous owner and is in overall good condition except for the valve train. At the time he was already unable to get a replacement cam, followers and rockers so he sent them off to be re-machined - at not fault of his own, the guys that did the job appear to have not known enough about these older motors and appear to have done a botch job. The followers were hollowed and the cam lobes were convex. So they were ground off flat whereas they apparently should be be slightly hollowed and the lobes slightly convex.
Long story short - for the sake of a bum cam, followers and rockers do I now turf and otherwise good motor and a conversion job that is superb for another motor conversion where I would have to replace the bell, clutch, mountings and modify a whole bunch of other stuff and then sit with a good few months sorting out all the niggles afterwards. Not even the numbers made sense in my case because the motor was otherwise in good nick. Then, although a minor issue but not insignificant, there's the bit about changing the details on the vehicle registration.
This past week I managed to source a cam, followers and rockers that were not too badly worn at a fairly reasonable price. They have been sent to a CT company (not Master Cams), who know these old motors and will re-machine my parts so that I don't have an overly long duration on the valves. It will be slightly warmer than standard but I will still be developing close to max torque just off the idle. They will also be case hardened. Besides the labour factor, the total cost in my case with gasket set included will be less than ½ of one of those re-conned motors in the link above and a mere fraction of another conversion. I might just have the ports polished as well while I have the heads off and may replace the original exhaust manifolds with branches.
But that's my situation, not yours. Depending on what is actually wrong with your motor, instead of trying to repair it, it might be worth your while to consider an upgrade to a more current motor, but it's not going to be a cheap exercise and the down time will be substantial. Alternatively, you can try those guys in your link and you might even be lucky and get a unit from them in a condition that will still give you years of good service. It's your call.