59 Apache drop

[resin addict]

I'm having the No Limit wide ride IFS installed on my 59 Apache, they say it'll drop the truck 4-5". I'm trying to figure out what tire size I'll need once that is done.
I'm assuming they mean it'll drop it 4-5" from stock height, the previous owner put on some tires that I'm sure are too big (in diameter) for stock, so I need to know what was the original tire size (diameter) so I can match this with a new rim and tire to actually get this 4-5" drop.
For example, it currently has tires that are almost 29" in diameter (on 15" rims...yes, it looks bad), which I'm sure has actually raised the truck, so even with the IFS and it's 4-5" drop, I'm actually only acomplishing a 2-3" drop if I keep this same tire size.
Thanks,
Randy