heres the oversimplified solution to all problems in the ...
get a 88-91 suburban inst. cluster with elec. speedometer. you cannot just snatch the speedo out becuase the PC board is different, and the housings are different. i myself have 2 and both are for sale 65+shipping. a very very simple repining of the factory inst. cluster harness and your all set. connect the VSS signal from the computer to the #18 pin of the connector, and call it done.
as far as the temp, autometer makes a probeless water temp sender, and adapter for the ls motors. it reads a tad incorrectly (15*) but whatever, im thinking of just taking the needle off, and resetting it by hand, or even trying to play with resistors.
autometer 2277 is the adapter
autometer 2259 is the probless. you dont want probe syle becuase it doesnt fit in the adapter, you would have to bore it out (becuase we did that to my friends swap), plus automtere asured me it reads the same.
anyway thats the solution to your problems and they are all cheap to get/do
clint