Personally, I would not drill a new tank to make it 1”
To maximize head pressure, I use 1” piping from the return pump... and than add a reducer coupler (link below) in the line near the end to fit the 3/4” bulkhead.
Slip x Slip. PVC Pipes for your plumbing needs. Use Schedule 80 Reducing Couplers to change plumbing size. More professional look than white Schedule 40 PVC. The golden rule of plumbing is that every job takes three trips to the store. While this can be frustrating locally it can be much worse...
www.bulkreefsupply.com
no pic of my set-up but I can take one later at home if u want