I have several dip-8 LM308s... they are not hard to find... I believe Small Bear has them.308's come as metal can versions, which tend to be less reliable, but if you get the lucky chip, it'll sound amazing
The stock 47pf cap would probably make the TL070 sound incredibly bright and might even cause it to oscillate/squeal. I never tried the NE5534 just the TL070 because it is so similar to the 308 with less noise. If you search diystomboxes.com for rat, tl070, lm308, compensation cap, etc. You will find more info concerning the rat than you would ever want to know.Fr8, if I put a TL070 in place with the same value cap as LM308, what happens ? Does it feed back or sound less than good ? Interesting you say its smoother, I certainly have no reason to doubt that. Do you have any rat TL070clips ? Ever try NE5534 ? I like the LM308, but am always on the quest for better sounding, better feeling and responding overdrives, as an alternative to cranking tube amps way up .