Lets break this down a bit.
first off, 3.55 gears in a big block dart will be ok for strip use, fine for spirited street driving and highway friendly.
I don't know what a fat isky cam is, I'm assuming you have some lopey *** idle. Unless you can provide the cam specs that doesn't really help.
I can guarantee you with absolute certainty that your 2600 stall converter isn't enough for the combo and will be the detriment to your driving experience. I'd go as far as to bet it's an off the shelf piece that if you are lucky might perform like an inefficient stock converter.
As far as tires, you can get any height and width you want in 15". Go to summit racing and just keep narrowing the search criteria down. I.e. tires -- 15" wheel dia -- height ---- section width, etc. Once you find your tire, you can buy it from there or shop around.
A 235 tire height (in a 15") will be dependent on the 2nd number, i.e. 235/50R15.
Use an RPM calculator such as the one at RMS suspension to figure the tire height you require for your desired cruise speed. I base everything off 60MPH RPM because the highway is where you can quickly become most unhappy with a car. I.e. I run a 28" or 29" tall tire with my 4.56 gears to achieve 2500rpm @ 60mph. This may or may not work out at the strip but street performance and function should always outweigh strip function in a street/strip car because that's where it will live most of the time.
Last a 235 radial is useless on that setup. Get a real tire under it. My advice would be a 26x10.50 sportsman pro which with a offset shackle fits with ease and will hook it up. If you are dead set on radials go with a drag radial on the widest wheel you can fit. radials require the widest wheel per tire section width to function properly.
