If it were me I'd call Kurt on this too.. (not affiliated justa friend)... "Light" for me seems to be an immediate "probably not that good an idea" off the top of my head but I could have that wrong.. If you want nice and flexy typically you do medium... That said he does sell light and he knows those spring rates and load carrying capacity better than anyone I know... Hope it helps!
RE distributors, I have done a lot of messing around with 2F distributors... First before all else start the truck and make sure the oil pressure gauge is working... Assuming it is, if you remove the distributor at all, make sure you always check the oil pressure gauge first after you restart it. If no oil pressure then turn the engine off immediately as its not getting oil! The distributor turns the oil pump.. Ask me how I know, uh, I have seized *two* (imagine how stupid I felt after the first time) 2F engines with distributors becoming unseated or not all the way in even though they felt 100% seated...
The best distributors IMO are the commonly called "Non USA" which is basically a '69-70 F engine distributor with the octane adjuster. This setup with an electronic aftermarket kit like Pertronix seems to be the best. You can usually find them cheap besides the $300 cost from Specter. I don't think I ever paid more than $50 for one but this was a good deal every time... Perhaps check the classifieds section of mud... And the other was a '79 distributor that was originally designed for smog but I ran desmogged and closed the ports on the distributor. This setup already has an electronic setup instead of points. Key in my opinion is to get rid of the points. Not so much that points wear out but distributor shafts develop microscopic amounts of play and it becomes harder to dial points, and some aftermarket companies make crappy points. You need to use a late FJ40/FJ60 or even a mini truck sealed coil/ignitor combo but these two units all work together very well. I hope this all isn't too confusing...
You want a vaccum advance distributor, not a vacuum retard, which almost all 70's era distributors are (vaccuum retard). Only the very early ('69 and earlier) and '79 and later are vacuum advance. A FJ60 distributor also works but the head on them is very large so you need a 2F side cover from a FJ60 too otherwise they don't fit. They are basically a '79 era distirbutor (curve, performance, etc) but with a larger head. The '79 and later also seal up nicely with a little silicone so can be used for water corssings/etc...
Also, it is not so much the strength of the spark but the timing of the spark. I'm not sure if Jim Chenowith is still in business(?) but he was someone who came up with new spark curves and can recurve factory Toyota distributors to optimum timing. This is what I would recommend, and it seems to be a noticable difference in power and efficiency... Or if you can find a performance engine shop locallt that does distributor work I think this goes a long way. Even the factory curve is off from where it should be. Hope it helps...
This is all how to "throw small things at an engine." It is sort of like building a bike light, costs a lot of money and in the end you have to wonder if its worth the cost for minimal gains but sometimes it is, assuming you start with a good base. In the end a 2F with a grand or two of goodies can feeled dialed and stronger and "plenty of power" so it can be worth it... The combo of a good strong carb, dist setup/ignition, and possibly even headers together can yield a good strong engine.... A truly solid/dialed 2F goes a long way in my opinion and is definetely a good candidate for a lifelong engine for a cruiser. Even though they are old school and usually guzzle...
Or do little cheap things for now if you are happy with it and perhaps plan for a swap later...
Cheers,
Andre