There are several mods you can do yourself, Call TransTech or transmart and order their performane bulletens. They'll guide you through the valve body mods (increase line pressure, flow rates and leak down after disengage, as well as alter lock in points). If your going to go into it, get a good quality HD kit (old style HD master kit, I forget the new terminology). It will help with better drum and piston seals, along with other aspects.

The main weak link is the converter. You can ask TransMart where to obtain specialty units, I don't rem where they used to come from. TransMart would order them and then resale to me, but they no longer resale outside itmes (so I'm told). The TQ you want is essentially an HO off road Toyota or Isuzu (rodeo I think) inside and Volvo outside (mount). One of the guys I worked with years ago went into his and noticed the shorter ring cuts (number of clutches). He ended up canabolizing some drums from a "dead core" (IE: one we got back on core, but was no core charge) that was either out of a 4wd Toyota or 4wd Isuzu. I don't remember the exact issue, but I think it was just one of the drums and the sealing rings to the shat were diff diameter. What ever the case, he ended up having to use the sealing rings from a GM kit. Don't rem which drum or which kit though, sorry. I do remember that it was enough of a difference that it would have burned out the friction plates in that drum had he not have.

Also courtosy of a friend in the UK, I now know that of the many different gov configurations, that one you have also came in some Toy trans and you can match it up & then order a gov tune kit for shifts to meet your needs.

All in all, you just need to do some reasearch. If you're gonna swap drums, make sure to mic everything between the new and the old. TransMart can even help you get on the right track to getting all the info you need. You may have to go through a few ops to get one who's willing to get you some contact info on ppl who can & will help. On their list is Frost Transmission, DO NOT bother to call them, they have been known to steer ppl wrong just to poke the "should'a brought it in" line. Sadly, I used to work for them.