What you can do, is increases the capacitance on the second and third stages. For an old Eico, without looking at the schematic X2 or more is not unreasonable. If you are going to build a cap bank. Buy a few extra. Lets say your can cap was 20-20-20uf , try 20-40-40uf . What I would do, is buy a handful of 10-20uf caps, decent ones are less than 2 bucks, each , less on E-bay. Start small, then add till you get the sound you like. Look to the after market ST70 setups for inspiration.

If you need to stick with the can cap format AES is making new ones…John