No need to Tee into lower rad hose at all. You cut the lower rad hose and install the heater into the hose and clamp it back together. You will need the correct size heater for you hose and I don't remember the I.D of the lower rad hose off hand, maybe 21/2''. I have done many and here are a few pointers:
-From now on I will ONLY use a T-bolt clamp like a Kodiak or a Greenline or whatever. The standard worm clamps just seem to sink into the rubber with all the heat that is produced by the heater, which is a lot. Then they just won't clamp hard enough and will leak. Then you have to drain all your coolant again and put proper clamps on. Happened to me a few times before I got smart.
-I have a 750w in my 84 and it does just fine. You would maybe want a 1000w if your way in the north. All are t-stat controlled and cycle on an off.
-You want it installed in the upper part of the lower rad hose so when the water gets warm (rises), the heat will travel into the block instead of heating up your rad, which is useless. If its installed right at the lowest part of the hose, half the heat will go into rad and half into block. So just mount it high on the hose
-And DON'T use the factory block heater port on your 84. That part of the block was a weak spot and was prone to crack until sometime in 85 when the reinforced the webbing around that port. Lets not send another good ol 6.9 block to the scrapper.
-They are easy to install, don't let them scare you. Just follow the above steps.