Having spent over 40 years with various 1600's including GTA's, with some seriously altered heads and other variations, I've found not a lot is to be gained over 7500. The port and bowl design, even with 42 mm intake valves will limit power up high or useable torque down low. Stock rods carefully prepped will begin to stretch above 4000f/m. Modified pumps with straight cut, long gears can deliver pressure and, more important, oil volume, above 7500, but stock geared pumps, start to loose pressure and oil volume as slow as 7200, with a usual 3 lb. pressure loss by 7500, dropping quickly beyond that. Individual engines will vary, and much can be gained by reducing reciprocating mass.
My engine building is restoration of old race engines, with a close eye on preservation.
Jim's above suggestion is very real. Who can know what internal stresses have built up over time in 40+ year old Veloce rods? I use "I" beam Carello's, lightened JE pistons, with the light wrist pins, moly coated skirts, gapless rings in 79 mm. Yes, I have gone to 80 mm, but the paper thin liner skirts are a little spooky. For 80 mm pistons, block liner bores need to be opened up with custom liners. Valve gear is altered to use titanium valves, single plug @ about 41 mm intake. copper bryllium seats and guides, and titanium upper spring retainers. Followers are DLH treated. Blocks are drilled as 5 oilers, and 4 holes are also drilled in the upper water manifold directed at the liners. There are plenty of discussions on crank work here on the BB. Same for oil pumps. Pump pressure and volume must be there at maximum constant expected engine speed. Proper assembly and run in with performance engines is important, a well thought out 1600 can live a long time at 7000 to 7500 RPM.
There are many pure race engine builders here on the BB. Alfar7 will have (I expect) some critical ideas that differ from the above. Send him a PM, and he can tell you how to keep them alive at even higher speeds
! Hope this helps.
Gordon Raymond