Of all the recent innovations within the hobby, the easy availability of sprung diesel bogies must rate very highly indeed. Both Penbits, as here, and Rumney Models (I have a set of their Warship bogies to build soon) have established a range of bogies for a variety of classes.
For a while now I've been working on Penbits bogies for a class 47 and a class 37, the latter can be seen here. The kits are very well designed and the brake gear is superb - a bit fiddly in places due to the small size of components, but it all goes together rather well. The one disadvantage of modelling diesel locos is that there is a lot of brake gear and it can get repetitive. A little and often approach works very well!
The Penbits bogies all complete and working very nicely; over the last couple of days I've added the cosmetic frames with their separate brake cylinders and steps. The brake cylinders are the last of my stock of Hornby Class 50 ones. The steps are modified from the Bachmann originals with PH Designs step treads epoxied on. As they come the PHD etch for the steps have the two lower the steps mis-spaced. So, whilst the solution isn't perfect, the overall effect is relatively pleasing. But at five quid a set for the steps, just using the treads isn't very cost effective - I used them as I had them in stock and had intended to use them for the model before realising the issue with them.
So the model is mechanically complete now, all the remains is to add the remaining details, and there are a lot of them, especially around the underframe - it could take a while!