Not sure if you have ever restored other Heathkits but they are famous for having carbon composition resistors that increase in value and go out of spec. I replaced quite a few in my SB200, DX60's, etc. This is a problem with carbon composition resistors and not a problem specific to Heathkit. The cheapest spectrum analyzer like tool is an RTL-SDR. They are available covering 100 kHz to 1.7 GHz for about $20. The important feature is that they provide a visual display of amplitude vs frequency like a spectrum analyzer so you can search a wide frequency range quickly for signals. As I recall the reason the SB200 does not have its grids grounded is so that C14 and C15 can be used to tune out the grid inductance of the 572's. One drawback is that 200 pF cannot provide a very good ground on the 160M band which is why most true grounded grid amplifiers cover 160M but the SB200 cannot.