I really like the idea of the th200r4 in the V8 RX7.
Which top end kit are you looking at? Hyd roller cam or hyd flat tappet cam?
The flat tappet "RPM" cam is nothing special.
The Edelbrock RPM Hyd roller version cam is not too bad.
If you could while you are measuring, measure the piston deck clearance @TDC.
From the outer high part of the piston not the dish.
(.025" ish +/-)
I have a few more heads to recomend.
GM Bowtie vortec GMPP pn#25534446 (assembled)
AFR 195 Eliminator #1034 (64cc)
AFR pn#912 "Vortec" Eliminator (new) look here
All These are way ahead of the Edelbrock E-Tecs
The AFR heads can be ordered factory direct with otion like chamber CC volume adjustment.
I think with the stock dished pistons you are going to want a 58-60 cc ish finished chamber volume.
With the car being so light weight and the high ratio rear cogs I would consider a (Street) solid lifter cam for this motor (roller or flat tappet).
You will need a high stall converter fo the Edelbrock RPM cams
I recomend a 3000 minimum stall and 3500 stall best. With converter full lock up function retained.
Here is my RX-7 V8 recipe recomendation.
AFR 195 Eliminators #1034
Edelbrock Performer RPM air gap manifold
Or Edelbrock Vic Jr manifold (one makes more low mid torque, the other makes a bit more top end power)
Holley-Demon- Proform 750 DP
Isky "Z-27" street mechanical flat tappet cam pn 201027
cam specs with 1.6 ratio rockers will be 282-282 247-247@.050" .540" gross lift 108LSA lash is .016" .018"
Summit 1.6 ratio roller rockers pn SUM-G6906
Yank or Vigilante 3500 stall lock up converter (TH-2004R)
Granny's SBC V-8 RX-7 headers