You might want to check page 17 of this PDF (page 5 of the promotional literature for the 1020S) : http://vintagemachinery.org/pubs/2379/4491.pdf
. Your 10hp motor will be plenty. Note the original Reeves drive had plenty of power drop-off, just like a VFD, and only put 1.5hp at the spindle at 400rpm running open belt. This chart is what I used to size the motors for my lathe.
When I did a VFD conversion on my 1030F I used 5.5kW (~7.4hp), 1800rpm motors (https://dealerselectric.com/00418ET3EAL112M.asp
also, wow the price on these has gone up >50% since 2017), driven by a 5hp TECO A510 VFD. The 5.5kW 1800rpm motors are 1.6hp at 400rpm, so a little better than the original Reeves drive. In retrospect I should've run the 7.5hp VFD, oops. Luckily the 7.5hp VFD has the same packaging as the 5hp VFD, so should be an easy drop-in replacement someday.
The 5hp VFD is ample; I have startups tuned to be quick, and adding a braking resistor allows the lathe to stop in a second or two, as well. With heavy cuts or largeish drills (>3/4"), the speed will slow a bit, especially when running in open belt. In the lowest back gear I've never noticed problems with the motor bogging, but maybe I just haven't pushed things hard enough. I've never stalled the motor or errored the VFD in a cut.
My VFD started to error out above ~3400rpm with the motors I chose, so that's my redline. So far I haven't missed the higher RPMs, and I do plenty of 5C work. Heck, an HLVH only goes to 3000rpm.
The biggest annoyance is the lathe has to be warmed up for 20-30min when running in a cold shop (<55degF or so) before it can be reliably started in open-belt. When the oil and bearings are cold the VFD struggles to get up to speed. Largely the warmup hasn't been an issue though; I just start my work in backgear or if I know I'm going to run the machine I start it as soon as I get to the shop. A larger VFD would surely reduce or eliminate this behavior (and allow even more aggressive startup/stops).
Some more conversion details in case they're useful to you:
I believe the metric-frame motors were the only option that fit through the cabinet door because they allowed me to put the wire box in the specific orientations required.
I used two separate, identical motors, one to drive the backgears and one to drive the open belt, and used the original FWD/REV contactor in the cabinet to switch the single VFD between the two motors (since you have to stop the spindle to switch between back gear and open belt anyways, this arrangement works fine). The contactor is controlled by a microswitch under the cover at the left end of the headstock that senses the position of the backgear selector knob. This way you just have to change the one gearbox lever to go between backgear and open belt, rather than the two selections the original drive required. (I also did this because the original back gear/open belt clutch assembly had problems on my lathe, so using this with a single VFD-driven motor would've been annoying).
The hardest part of the conversion (since I'm not an electrical engineer) was getting the original tach to work (I was willing to make big changes under the hood, but the only external change I wanted was replacing the speed control buttons with a potentiometer). The tach is 0-28V, but the VFD outputs 0-10V analog for speed. I had to make a small op-amp circuit to multiply the VFD speed signal by 2.8 to get the tach to work.
All the other functions of the lathe (spindle stop due to threading, etc) were straightforward to wire into the VFD and preserve functionality with.
Oh yeah I added a bicycle disc brake with 160mm rotor to the backgear motor pulley to allow me to lock the spindle when changing chucks (since my machine is L-0). The brake is necessary; even with the lathe in its lowest backgear you need the brake active to loosen/tighten the spindle nut. You can probably get away without the brake since your machine is camlock. Someday I'll integrate the brake control into a foot pedal on the lathe (with microswitch to turn off the motor of course), but that's a low-priority project.
If for some reason you want the original Reeves drive, I still have the motor and hardware removed from my lathe. I'm sure we could make a deal.
That was a lot of words but I hope some of them were useful.