X 2 what Wageslave said.
From a google search I just did,the TH200 has a 2.74:1 first gear ratio.Combine that with your 2.14:1 rear gear ratio gives you a very poor SLR,or Starting Line Ratio.
Using the Wallace Racing SLR calculator with a 26.5 inch tire gives you a SLR of 4.28.
Closer to a SLR of 9 would be a huge improvement and would be a big "kick in the pants".
And,AFAIK,some Vortec heads will bolt on to your 305,although specific intake manifolds and valve covers must be used,and the heads will need to be milled to keep the compression up where it needs to be.
I copied and pasted this from HotRod Network;
"The Class Of The Heads
Chevy 305s came with only 1.84-inch intake and 1.50-inch exhaust valves. Fortunately, there is an effective upgrade available in the form of ’96-’97 Chevy truck L31 Vortec heads with 1.94-/1.50-inch valves. The cast-iron heads’ intake and exhaust ports are similar to the late-model Corvette aluminum LT1 heads, but unlike the LT1 heads, they bolt onto conventional small-blocks. The Vortec’s greatest improvement is on the intake side, which is why we chose the dual-pattern cam with its slightly larger exhaust lobes.
There are several minor hassles when using Vortec heads. First, they have a unique intake manifold bolt-pattern requiring a dedicated (and more costly) GM or aftermarket intake. Also, early small-blocks must switch to ’87-and-later center-bolt valve covers and late-model guided rocker arms. The heads’ 64cc chambers must be milled to avoid compression loss on a 305, and the larger-diameter chamber outline requires 350 head gaskets, which could also cause reduced compression. To solve this, we milled the heads 0.045-inch and used thin 0.015-inch head gaskets and got just over 10.0:1 compression. We had no detonation problems on the dyno even with 89-octane gas."
A set of these heads and a matching camshaft will be a step in the right direction.
I am not a big fan of Comp Cams,but I do like the Bullet Racing line of cams;
Bullet Cams specializes in camshafts and valve train components for serious racers
www.bulletcams.com
Your best bet would be to call and talk to one of the experts there,Tim is who I would ask for.
Matching valve train components are also recommended.The wrong valve springs could destroy a new engine in a hurry.
Guy