TKL = 1978 350, or a 1978 400, or a 1980 350. A 400 would have some material removed from the outside diamter of the front harmonic balancer, and also added weight on the flywheel for external balanceing. Also if you rub your hand down the side of the block you would feel lumps where each of the cylinders are.
If the side of the block is smooth it's a 350. Could you post the casting numbers on the back of the block? They're located on the drivers side of the block between the head and the bellhousing. 400 casting numbers, 3951511, 3951509, 330817. Hope this helps.
Brian
