Alright checked the rest of my IIvx form factor machines and here goes:
Q650 with top vents only, has frame support, s/n FC4031JN1M1
Centris 650 has top and side vents, no frame support, s/n F1305BTNCC5
Performa 600 has top and side vents, no frame support, s/n F2247M8J3BN