Any benefit to upgrading the top loader bell housing to a T5 bell when doing a T5 conversion?

If your spending money, Get a scatter shield.
I have never had a clutch / flywheel explode and come thru the scatter shield. Never been in a serious car accident but always wear a seatbelt. Adapter plates are for when you don't have a better option. I only have experience with the old Lakewood's, but the new Quick times look good.

I have the t5 five speed now in my 65 and use a scatter shield for a t5 (85-93 mustang) and a modern clutch cable conversion. Been in 10 yrs and a hundred + 1/4 mile (low 13s) passes and never a problem with it. My buddy (65) did the same with the hydraulic set up and was unhappy with the fire wall flexing. Switched to a cable and is happy. I used auto headers shorty headers and heat sleeved the cable.