the tank can be drilled if there isnt a tempered bottom pane in there, 9 out of 10 times there is.
I know its overkill but that size tank you might want to just research wet/dry filters for it. I got a 45g tall tank for discus and got a 175g capable sump system on it with a CPR overflow ( i think its the 201)
its got eco complete in it now, and water. only change.
here is the sump
This is my old mans tank, i got him the glass coffin, canopy, tank and stand.
in two weeks he has put over 1200 bucks into the tank and he hasnt bought a single fish yet. He also like you has been out of the game for a while, 20 years exactly this year and he was eyeballing 300g but that wasnt in my budget unfortunetly but we are working with what we got.
Id run a sump w/ overflow if you cant drill it sumps require less maintence then a hob
or canister and also eliminate the risk of toxin backflush when there is a power outage.
PM me and I can get your email and send you things that helped him make his decisions. he kept fish from 1967 to 1990 bred all sorts of fish, kept monster cichlids and just had to quit when he got orders to deploy in 1990 for the sandbox. It took me getting him the glass box to get back into it but he did and well you can see above what is going on. Any of us here would be happy to help you out.
in the end its your tank and you are the one who has to look at it daily and you also get what you pay for in this hobby, almost any deal is never too good to be true, you find a deal grab it.
Do you have a budget for this build and is it reasonable?